Mixed mode assembly is built against version v2 0 50727 of the runtime

Question

I m getting the following exception      Mixed mode assembly is built against version    v2 0 50727  of the runtime and cannot be loaded in the 4 0 runtime without additional configuration information    as I was trying to export crystal report from my WPF program      I have added the following in the app config already      lt startup useLegacyV2RuntimeActivationPolicy  true  gt     lt supportedRuntime version  v4 0  sku   NETFramework Version v4 0   gt   lt  startup gt   lt runtime gt     lt NetFx40 LegacySecurityPolicy enabled  true   gt   lt  runtime gt    Any experts can help      Reference I found   http   www davidmoore info 2010 12 17 running-net-2-runtime-applications-under-the-net-4-runtime

User · Answer

I actually had this identical issue with the inverse solution. I had upgraded a .NET project to .NET 4.0 and then reverted back to .NET 3.5. The app.config in my project continued to have the following which was causing the above error in question:

<startup>
  <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>

The solution to solve the error for this was to revert it back to the proper 2.0 reference as follows:

<startup>
  <supportedRuntime version="v2.0.50727"/>
</startup>

So if a downgrade is producing the above error, you might need to back up the .NET Framework supported version.

User · Answer

Try to use another config file  not the one from your project  and RESTART Visual Studio   C  Program Files  x86  Microsoft Visual Studio 11 0 Common7 IDE CommonExtensions Microsoft TestWindow vstest executionengine x86 exe config  32-bit    or  C  Program Files  x86  Microsoft Visual Studio 11 0 Common7 IDE CommonExtensions Microsoft TestWindow vstest executionengine exe config  64-bit

User · Answer

Enabling the legacy from app config didn t work for me  For unknown reasons  my application wasn t activating V2 runtime policy  I found a work around here   Enabling the legacy from app config is a recommended approach but in some cases it doesn t work as expected  Use the following code with in your main application to force Legacy V2 policy   public static class RuntimePolicyHelper   public static bool LegacyV2RuntimeEnabledSuccessfully   get  private set     static RuntimePolicyHelper         ICLRRuntimeInfo clrRuntimeInfo            ICLRRuntimeInfo RuntimeEnvironment GetRuntimeInterfaceAsObject              Guid Empty               typeof ICLRRuntimeInfo  GUID       try               clrRuntimeInfo BindAsLegacyV2Runtime            LegacyV2RuntimeEnabledSuccessfully   true            catch  COMException                   This occurs with an HRESULT meaning              A different runtime was already bound to the legacy CLR version 2 activation policy           LegacyV2RuntimeEnabledSuccessfully   false            ComImport   InterfaceType ComInterfaceType InterfaceIsIUnknown    Guid  BD39D1D2-BA2F-486A-89B0-B4B0CB466891    private interface ICLRRuntimeInfo       void xGetVersionString        void xGetRuntimeDirectory        void xIsLoaded        void xIsLoadable        void xLoadErrorString        void xLoadLibrary        void xGetProcAddress        void xGetInterface        void xSetDefaultStartupFlags        void xGetDefaultStartupFlags          MethodImpl MethodImplOptions InternalCall  MethodCodeType   MethodCodeType Runtime       void BindAsLegacyV2Runtime

User · Answer

Try to use this exact startup tag in your app config under configuration node   lt startup useLegacyV2RuntimeActivationPolicy  true  gt       lt supportedRuntime version  v4 0  sku   NETFramework Version v4 0   gt       lt requiredRuntime version  v4 0 20506    gt     lt  startup gt

User · Answer

The exception clearly identifies some  NET 2 0 50727 component was included in  NET 4 0  In App config file use this    lt startup useLegacyV2RuntimeActivationPolicy  true    gt     It solved my problem

User · Answer

For me this was thrown when running unit tests under MSTest  VS2015   Had to add    lt startup useLegacyV2RuntimeActivationPolicy  true  gt   lt  startup gt    in   C  Program Files  x86  Microsoft Visual Studio 14 0 Common7 IDE CommonExtensions Microsoft TestWindow TE ProcessHost Managed exe config  Mixed-Mode Assembly MSTest Failing in VS2015

User · Answer

If the error happens with error column  File  as SGEN  then the fix needs to be in a file sgen exe config  next to sgen exe  For example  for VS 2015  create C  Program Files  x86  Microsoft SDKs Windows v10 0A bin NETFX 4 6 Tools sgen exe config  Minimum file contents   lt configuration gt  lt startup useLegacyV2RuntimeActivationPolicy  true   gt  lt  configuration gt   Source  SGEN Mixed mode assembly

User · Answer

Please add attribute useLegacyV2RuntimeActivationPolicy  true  in your applications app config file   Old Value     lt startup gt       lt supportedRuntime version  v4 0  sku   NETFramework Version v4 5 1   gt     lt  startup gt    New Value     lt startup useLegacyV2RuntimeActivationPolicy  true  gt       lt supportedRuntime version  v4 0  sku   NETFramework Version v4 5 1   gt     lt  startup gt    It will solve your problem

[.net] Mixed mode assembly is built against version ‘v2.0.50727' of the runtime

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