I got this on a Win2008R2 x64bit server where I’m running a 32bit app.Details: Could not load file or assembly ‘FIXForge.NET.FIX.Engine-net-4.0.dll’ or one of its dependencies. The specified module could not be found.” So I figured that all I have to do was load it into the Global Assembly with gacutil /i and I’d be ok. But… “Failure adding assembly to the cache: This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded”. How can this be? I was using SDK 6, so I installed SDK 7.1 and tried again with the same result. However if you switch to the ‘proper’ version of gacutil it will work ok. Go to C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\NETFX 4.0 Tools\x64 Now gacutil /i will register your dll. Use the /l [assembly name] option after too see the reaults (take “.dll”) off the end of the assembly name.