[c#] Duplicate AssemblyVersion Attribute

I have a project that generates following error on compilation:

error CS0579: Duplicate 'AssemblyVersion' attribute

I have checked the file AssemblyInfo.cs and it looks like there is no duplication there.

I found this article on MSDN which addresses a similar problem and following the suggestion in this article fixes the problem as well.

Can anyone tell me what's going on here? Does it happen only in case of having two or more projects with classes having similar names? Or is it something else?

This issue is a reference conflict which is mostly peculiar to VS 2017.

I solved this same error by simply commenting out lines 7 -14 as well as Assembly version codes at the bottom of the page on AssemblyInfo.cs

It removed all the duplicate references and the project was able to build again.

My error was that I was also referencing another file in my project, which was also containing a value for the attribute "AssemblyVersion". I removed that attribute from one of the file and it is now working properly.

The key is to make sure that this value is not declared more than once in any file in your project.

I have being struggling with this issue, but my problem was much easier to solve.

I had copied OBJ folder to "OBJ___" name to do some compilation tests.

So, I don't know why, this folder was being also compiled, creating the assembly attributes duplication.

I simply deleted the "OBJ___" folder and could compile successfuly.

In my case, there where a subfolder in a project that was a project folder it self:

• file system:

  • c:\projects\webapi\wepapi.csproj
  • c:\projects\webapi\tests\wepapitests.csproj

• solution

  • webapi (folder and project)
    • tests (folder)
  • tests (folder and project)

Then i had to remove the subfolder "tests" from the "webapi" project.

I got this error when I did put 2 projects in the same directory. If I have a directory with an solution and I put a separate Web and Data directory in it compiles right.

There must be already a AssemblyInfo.cs file in the project here:

To solve: - Delete any one AssemblyInfo.cs

In my case, some temporary *.cs files generated during compilation got accidentally added to the project.

The files were from the obj\Debug directory, so they definitely shouldn't have been added to the solution. A *.cs wildcard went a little crazy and added them incorrectly.

Deleting these files fixed the problem.

I had this issue when my main project was in the same folder as the solution, then I had a separate project in the same solution located in a sub folder, and that separate project used the main project as a reference. This caused the main project to detect the sub folder bin & obj folders which created duplicate references.

I came across the same when tried add GitVersion tool to update my version in AssemblyInfo.cs. Use VS2017 and .NET Core project. So I just mixed both worlds. My AssemblyInfo.cs contains only version info that was generated by GitVersion tool, my csproj contains remaingin things. Please note I don't use <GenerateAssemblyInfo>false</GenerateAssemblyInfo> I use attributes related to version only (see below). More details here AssemblyInfo properties.

AssemblyInfo.cs

[assembly: AssemblyVersion("0.2.1.0")]
[assembly: AssemblyFileVersion("0.2.1.0")]
[assembly: AssemblyInformationalVersion("0.2.1+13.Branch.master.Sha.119c35af0f529e92e0f75a5e6d8373912d457818")]

my.csproj contains all related to other assemblyu attributes:

<PropertyGroup>
...
<Company>SOME Company </Company>
<Authors>Some Authors</Authors>
<Product>SOME Product</Product>
...
<GenerateAssemblyVersionAttribute>false</GenerateAssemblyVersionAttribute>
<GenerateAssemblyFileVersionAttribute>false</GenerateAssemblyFileVersionAttribute><GenerateAssemblyInformationalVersionAttribute>false</GenerateAssemblyInformationalVersionAttribute>

My error occurred because, somehow, there was an obj folder created inside my controllers folder. Just do a search in your application for a line inside your Assemblyinfo.cs. There may be a duplicate somewhere.

This usually happens for me if I compiled the project in Visual Studio 2017 & then I try to rebuild & run it with .NET Core with the command line command "dotnet run".

Simply deleting all the "bin" & "obj" folders - both inside "ClientApp" & directly in the project folder - allowed the .NET Core command "dotnet run" to rebuild & run successfully.

I got the error Just after switching from .NET Framework to .NET Core. I have 2 class library projects in my Visual Studio solution. I realized that 1 of the projects has a file named AssemblyInfo.cs while the other project does not have the file. The file is located under the Properties folder. I simply delete the Properties folder and all works fine.

obj\Debug\netstandard2.0\PacktLibrary.AssemblyInfo.cs(15,12): error CS0579: Duplicate 'System.Reflection.AssemblyConfigurationAttribute' attribute [c:\Users\John_Tosh1\Documents\C#8.0and.NetCore3.0\Code\Chapter05\PacktLibrary\PacktLibrary.csproj]
obj\Debug\netstandard2.0\PacktLibrary.AssemblyInfo.cs(16,12): error CS0579: Duplicate 'System.Reflection.AssemblyFileVersionAttribute' attribute [c:\Users\John_Tosh1\Documents\C#8.0and.NetCore3.0\Code\Chapter05\PacktLibrary\PacktLibrary.csproj]
obj\Debug\netstandard2.0\PacktLibrary.AssemblyInfo.cs(17,12): error CS0579: Duplicate 'System.Reflection.AssemblyInformationalVersionAttribute' attribute [c:\Users\John_Tosh1\Documents\C#8.0and.NetCore3.0\Code\Chapter05\PacktLibrary\PacktLibrary.csproj]
obj\Debug\netstandard2.0\PacktLibrary.AssemblyInfo.cs(18,12): error CS0579: Duplicate 'System.Reflection.AssemblyProductAttribute' attribute [c:\Users\John_Tosh1\Documents\C#8.0and.NetCore3.0\Code\Chapter05\PacktLibrary\PacktLibrary.csproj]
obj\Debug\netstandard2.0\PacktLibrary.AssemblyInfo.cs(19,12): error CS0579: Duplicate 'System.Reflection.AssemblyTitleAttribute' attribute [c:\Users\John_Tosh1\Documents\C#8.0and.NetCore3.0\Code\Chapter05\PacktLibrary\PacktLibrary.csproj]
obj\Debug\netstandard2.0\PacktLibrary.AssemblyInfo.cs(20,12): error CS0579: Duplicate 'System.Reflection.AssemblyVersionAttribute' attribute [c:\Users\John_Tosh1\Documents\C#8.0and.NetCore3.0\Code\Chapter05\PacktLibrary\PacktLibrary.csproj]

I believe my Library folder was corrupted by an inadvertent creation of another class library.I deleted the library an all associated file but the problem persisted. I found a workaround by deleting ALL bin and obj folders in the directory. The build was ok previously but found a subfolder that had the same assemblyinfo.cs file.

When converting an older project to .NET Core, most of the information that was in the AssemblyInfo.cs can now be set on the project itself. Open the project properties and select the Package tab to see the new settings.

The Eric L. Anderson's post "Duplicate ‘System.Reflection.AssemblyCompanyAttribute’ attribute" describes 3 options :

• remove the conflicting items from the AssemblyInfo.cs file,
• completely delete the file or
• disable GenerateAssemblyInfo (as suggested in another answer by Serge Semenov)

I found this answer on msdn, that explains marking the file as Content and then Copy to Output = If Newer. See article below:

https://social.msdn.microsoft.com/Forums/en-US/8671bdff-9b16-4b49-ba9e-227cc4df31b2/compile-error-cs0579-duplicate-assemblyversion-attribute?forum=vsgatk

GH

Starting from Visual Studio 2017 another solution to keep using the AssemblyInfo.cs file is to turn off automatic assembly info generation like this:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
  </PropertyGroup>
</Project>

I personally find it very useful for projects which need to support both .NET Framework and .NET Standard.

I ran into this recently with no changes to source, but after experimenting with some new project references. I got into a state where this error was appearing even after reverting all changes in the branch.

Cleaning the branch resolved it for me:

git clean -xfd

If you're having this problem in a Build Pipeline on Azure DevOps, try putting the Build Action as "Content" and Copy to Output Directory equal to "Copy if newer" in the AssembyInfo.cs file properties.

I had the same error and it was underlining the Assembly Vesrion and Assembly File Version so reading Luqi answer I just added them as comments and the error was solved

// AssemblyVersion is the CLR version. Change this only when making breaking    changes
//[assembly: AssemblyVersion("3.1.*")]
// AssemblyFileVersion should ideally be changed with each build, and should help identify the origin of a build
//[assembly: AssemblyFileVersion("3.1.0.0")]

Yet another solution when upgrading core to VS2017 is to remove them in the properties\assemblyinfo.cs file.

Since they now are stored in the project.

For me it was that AssembyInfo.cs and SolutionInfo.cs had different values. So check these files as well. I just removed the version from one of them.

Edit you AssemblyInfo.cs and #if !NETCOREAPP3_0 ... #endif

using System.Reflection;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
// General Information about an assembly is controlled through the following
// set of attributes. Change these attribute values to modify the information
// associated with an assembly.

#if !NETCOREAPP3_0  

[assembly: AssemblyTitle(".Net Core Testing")]
[assembly: AssemblyDescription(".Net Core")]
[assembly: AssemblyConfiguration("")]
[assembly: AssemblyCompany("")]
[assembly: AssemblyProduct(".Net Core")]
[assembly: AssemblyCopyright("Copyright ©")]
[assembly: AssemblyTrademark("")]
[assembly: AssemblyCulture("")]

// Setting ComVisible to false makes the types in this assembly not visible
// to COM components.  If you need to access a type in this assembly from
// COM, set the ComVisible attribute to true on that type.
[assembly: ComVisible(false)]

// The following GUID is for the ID of the typelib if this project is exposed to COM
[assembly: Guid("000b119c-2445-4977-8604-d7a736003d34")]

// Version information for an assembly consists of the following four values:
//
//      Major Version
//      Minor Version
//      Build Number
//      Revision
//
// You can specify all the values or you can default the Build and Revision Numbers
// by using the '*' as shown below:
// [assembly: AssemblyVersion("1.0.*")]
[assembly: AssemblyVersion("1.0.0.0")]
[assembly: AssemblyFileVersion("1.0.0.0")]

#endif