The default XML namespace of the project must be the MSBuild XML namespace

Question

I cloned the ASP NET Core SignalR Repo locally  and try opening the solution from within the following environment   IDE  Microsoft Visual Studio Enterprise 2015 Version 14 0 25431 01 Update 3 Microsoft  NET Framework Version 4 6 01055   DOT NET CLI    dotnet --info  NET Command Line Tools  1 0 0-preview2-1-003177   Product Information   Version             1 0 0-preview2-1-003177  Commit SHA-1 hash   a2df9c2576  Runtime Environment   OS Name      Windows  OS Version   6 1 7601  OS Platform  Windows  RID          win7-x64   I end up seeing a lot of these kinds of error messages         Repos SignalR src Microsoft AspNetCore SignalR Microsoft AspNetCore SignalR csproj     error    The default XML namespace of the project must be the   MSBuild XML namespace  If the project is authored in the MSBuild 2003   format  please add   xmlns  http   schemas microsoft com developer msbuild 2003  to the    element  If the project has been authored in the old 1 0 or   1 2 format  please convert it to MSBuild 2003 format      Repos SignalR src Microsoft AspNetCore SignalR Microsoft AspNetCore SignalR csproj   I want to know how to fix this the correct way

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I was getting the same messages while I was running just msbuild from powershell   dotnet msbuild    project csproj  worked for me

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DavidG s answer is correct  but I would like to add that if you re building from the command line  the equivalent solution is to make sure that you re using the appropriate version of msbuild  in this particular case  it needs to be version 15    Run msbuild    to see which version you re using or where msbuild to check which location the environment takes the executable from and update  or point to the right location of  the tools if necessary   Download the latest MSBuild tool from here

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I ran into this issue while opening the Service Fabric GettingStartedApplication in Visual Studio 2015  The original solution was built on  NET Core in VS 2017 and I got the same error when opening in 2015   Here are the steps I followed to resolve the issue    Right click on  load Failed  project and edit in visual studio  Saw the following line in the Project tag   lt Project Sdk  Microsoft NET Sdk Web   gt  Followed the instruction shown in the error message to add xmlns  http   schemas microsoft com developer msbuild 2003  to this tag   It should now look like    lt Project Sdk  Microsoft NET Sdk Web  xmlns  http   schemas microsoft com developer msbuild 2003  gt     Reloading the project gave me the next error  yours may be different based on what is included in your project       Saw that None element had an update attribute as below    lt None Update  wwwroot      Views      Areas    Views  gt     lt CopyToPublishDirectory gt PreserveNewest lt  CopyToPublishDirectory gt   lt  None gt   Commented that out as below    lt  -- lt None Update  wwwroot      Views      Areas    Views  gt     lt CopyToPublishDirectory gt PreserveNewest lt  CopyToPublishDirectory gt   lt  None gt -- gt   Onto the next error  Version in Package Reference is unrecognized  Saw that Version is there in csproj xml as below  Additional PackageReference lines removed for brevity     Stripped the Version attribute   lt PackageReference Include  Microsoft AspNetCore Diagnostics    gt   lt PackageReference Include  Microsoft AspNetCore Mvc    gt   I now get the following     Bingo  The visual Studio One-way upgrade kicked in  Let VS do the magic    The Project loaded but with reference lib errors    Fixed the reference lib errors individually  by removing and replacing in NuGet to get the project working    Hope this helps another code traveler  -D

User · Answer

The projects you are trying to open are in the new  NET Core csproj format  This means you need to use Visual Studio 2017 which supports this new format   For a little bit of history  initially  NET Core used project json instead of   csproj  However  after some considerable internal deliberation at Microsoft  they decided to go back to csproj but with a much cleaner and updated format  However  this new format is only supported in VS2017   If you want to open the projects but don t want to wait until March 7th for the official VS2017 release  you could use Visual Studio Code instead

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If getting this error trying to build  Net Core 2 0 app on VSTS then ensure your build definition is using the Hosted VS2017 Agent queue

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if the project is not a big     1- change the name of folder  project    2- make a new project with the same project  before renaming    3- add existing files from the old project to the new project  totally same   same folders   same names         4- open the  the new project file  as xml   and the old project   5- copy the new project file  xml content   and paste it in the old project file   6- delete the old project   7- rename the old folder project to old name

[asp.net-mvc] The default XML namespace of the project must be the MSBuild XML namespace

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