Failed to start NUnit test.

Question

I installed NUnit 2.6.1 and tried to run a simple test on Windows 7 x64. This throws an exception

An attempt was made to download a program with the wrong format. You may be trying to load an assembly built with a later version of the CLR than the version under which NUnit is currently running (2.0.50727) or trying to load a 64-bit assembly into a 32-bit process.

This is rather strange because nunit.exe.config looks below

  <?xml version="1.0" encoding="utf-8" ?> - <configuration> - <!-- The GUI only runs under .NET 2.0 or higher. The useLegacyV2RuntimeActivationPolicy setting only applies under .NET 4.0 and permits use of mixed mode assemblies, which would otherwise not load correctly. --> - <startup useLegacyV2RuntimeActivationPolicy="true"> - <!-- Comment out the next line to force use of .NET 4.0 --> - <!-- <supportedRuntime version="v2.0.50727" /> --> <supportedRuntime version="v4.0.30319" /> </startup> - <runtime> - <!-- Ensure that test exceptions don't crash NUnit --> <legacyUnhandledExceptionPolicy enabled="1" /> - <!-- Run partial trust V2 assemblies in full trust under .NET 4.0 --> <loadFromRemoteSources enabled="true" /> - <!-- Look for addins in the addins directory for now --> - <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1"> <probing privatePath="lib;addins" /> </assemblyBinding> </runtime> </configuration> 

Answer 1

This is not like a problem with NUnit. It looks like your unit test assemblies are not built for a 32-bit process. Are you sure your unit test builds are built for 32 bits? If NUnit runs on 32 bits and your builds are built on 64 bits (or not built like Any CPU), you will get this problem. The calling application determines the bit depth required for assembly. You cannot use a 64-bit dll with a 32-bit process and vice versa.

The only reason I mention this is because your question says you are trying to run a test. If NUnit was configured incorrectly, it will not even start.