An attempt was made to load a program with an incorrect format even when the platforms are the same

Question

I m calling functions from a 32-bit unmanaged DLL on a 64-bit system  What I get is      BadImageFormatException  An attempt was made to load a program with an incorrect format   Exception from HRESULT  0x8007000B    At first  I had my projects set to the Any CPU platform  so I changed them both to x86  but this error is still occurring  That s really the only fix I know for this   The DLLs aren t corrupt or anything  because I can use them with other programs  that I don t have the source to   I thought that perhaps it wasn t finding a dependency  but I checked and they re all there  Plus  wouldn t it throw a DllNotFoundException in that case   What else can I do  And before you say  Use a 64-bit unmanaged DLL instead   let me point out that there isn t one

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I got this issue solved in the  Windows  way  After checking all my settings  cleaning the solution and rebuilding it  I simply close the solution and reopened it  Then it worked  so VS probably didn t get rid of some stuff during cleaning   When logical solutions don t work  I usually turn to illogical  or seemingly illogical  ones  Windows doesn t let me down

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If you encounter this error when you click green arrow button to run the application  but still want to run the app in 64 bit  You can do this in VS 2013  2015  2017  and 2019  Go to  Tools   Options   Projects and Solutions   Web Projects   Use the 64 bit version of IIS Express

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In Visual Studio  Right Click your project -  On the left pane click the Build tab     under Platform Target select x86  or more generally the architecture to match with the library you are linking to     I hope this helps someone

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If you are importing unmanaged DLL then use   CallingConvention   CallingConvention Cdecl    in your DLL import method

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If you are using Any CPU  you might encounter this issue if the Prefer 32-bit option is checked     Make sure you uncheck this option in the project s property s Build tab

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In my case  I am using a tiny  exe that reloads the referenced DLLs via Reflection  So I just do these steps which saves my day   From project properties on solution explorer  at build tab  I choose target platfrom x86

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I just had this problem also  Tried all the suggestions here  but they didn t help    I found another thing to check that fixed it for me  In Visual Studio  right-click on the project and open  Properties   Click on the  Compile   or  Build   tab and then click on  Advanced Compile Options  at the bottom    Check the dropdown  Target CPU   It should match the  Platform  you are building  That is   if you are building  Any CPU  then  Target CPU  should say  Any CPU   Go through all of your Platforms by making them active and check this setting

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In my case  I was running tests through MSTest and found out that I was deploying both a 32-bit and 64-bit DLL to the test directory  The program was favoring the 64-bit DLL and causing it to fail   TL DR Make sure you only deploy 32-bit DLLs to tests

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Building on the answer of  paibamboo  He said  Go to  Tools   Options   Projects and Solutions   Web Projects   Use the 64 bit version of IIS Express  My coworker had this box checked  he explicitly looked for it   but had the error message in question  After some hours he unchecked the box and checked it again  Lo and behold  The code now ran with success   It seems  that there are two places where the state of this box ist saved which became out of sync  Un- and rechecking it synced it again   Question for more knowledgable users  Was there an update or something last week  for VS 2015  which de-synced the states

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We were having the same issue in  NET core  The solution was to download 32-bit  netcore runtime  and having your project target x86  In your csproj file add     lt PropertyGroup gt       lt PlatformTarget gt x86 lt  PlatformTarget gt       lt  PropertyGroup gt      lt PropertyGroup gt       lt RunCommand Condition     PlatformTarget       x86   gt   MSBuildProgramFiles32  dotnet dotnet lt  RunCommand gt         lt  PropertyGroup gt    This was used for a Windows machine  you d have to adjust paths and such for Linux OSX

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In my case it was wrong content of the file  DLL was downloaded from the web  but content of the DLL was HTML page  D Try to check if it is binary file  if it seems like correct DLL

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Also see this answer  which solved the same problem for me   Posted by Luis Mack on 5 12 2010 at 8 50 AM I ve found the same problem  only for a specific project when compiling on a 64-bit machine  A fix that SEEMS to work is to manually alter one character in the image stream EVERY TIME the usercontrol or form is edited in the designer  AAEAAAD     AQAAAAAAAAAMAgAAAFdTeXN0ZW0uV2luZG93cy5Gb3JtcywgVmVyc2lvbj00LjAuMC4w  Change to  AAEAAAD     AQAAAAAAAAAMAgAAAFdTeXN0ZW0uV2luZG93cy5Gb3JtcywgVmVyc2lvbj0yLjAuMC4w  That is 00LjAuMC4w back to 0yLjAuMC4w at the end of the line  00 back to 0y

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In my case I was using a native DLL in C   This DLL depended on couple of other DLLs that were missing  Once those other DLLs were added everything worked

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If you try to run 32-bit applications on IIS 7  and or 64-bit OS machine   you will get the same error  So  from the IIS 7  right click on the applications  application pool and go to  advanced settings  and change  Enable 32-Bit Applications  to  TRUE    Restart your website and it should work

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Somehow  the Build checkbox in the Configuration Manager had been unchecked for my executable  so it was still running with the old Any CPU build  After I fixed that  Visual Studio complained that it couldn t debug the assembly  but that was fixed with a restart

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1 Go to  Tools   Options   Projects and Solutions   Web Projects   Use the 64 bit version of IIS Express  2  change below setting for web service project

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A bit off topic for this post  but searching for this error message brought me here    If you are building through team system and getting this error  the build definition process tab has a  MSBuild Platform  setting  If this is set to  Auto   you may experience this problem  Changing it to  X86  can also resolve the error

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I was able to fix this issue by matching my build version to the  NET version on the server   I double clicked the  exe just to see what would happen and it told me to install 4 5      So I downgraded to 4 0 and it worked   So make sure your versions match   It ran on my dev box fine  but server had older  NET version

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With Visual Studio 2019 I had a similar issue when I wanted to run tests  MSTest directly from VS   In my case I only had an x64 native DLL and I received this error message  First  I thought it is because Visual Studio runs as x86 but this page helped me to solve the issue  Run unit test as a 64-bit process It says  Set your projects to Any CPU Explicitly define processor architecture  I did both  I explicitly set x64  and then my tests started to work

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We had a similar issue and we managed to fix it by setting the Platform target to x86

[.net] "An attempt was made to load a program with an incorrect format" even when the platforms are the same

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