I am following this guide to installing and using MSpec, but at the step where he runs MSpec for the first time, I get the following error:
Could not load file or assembly 'file:///[...]\Nehemiah\Nehemiah.Specs\bin\Debug\Nehemiah.Specs.dll' or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded.
I have - to my knowledge - done everything more or less exactly like he did up to this step, except where differences arise because he's using VS2008 and I'm using VS2010, and everything has worked so far. The project Nehemijah.Specs (and the entire solution) builds without problem, both in Visual Studio and on my build server, and I can't find anything useful in Event Viewer (although I might not be looking in the right place here...)
What to do?
It appears you're compiling the Nehemiah.Specs.dll assembly against the .NET Framework 4. In order to run your specifications you need the .NET 4 build of MSpec which contains a console runner (mspec.exe) that is suitable for this version of the framework. You can find the a zip file containing the build on CodeBetter's CI server.
Other possibilities of running .NET 4 spec assemblies are
Runners for both tools are also included in the distribution.