Note that even if the DLL is in your path. If that DLL relies on other DLLs that are NOT in your path, you can get the same error. Windows could not find a dependency in this case. Windows is not real good at telling you what it could not find, only that it did not find something. It is up to you to figure that out. The Windows dll search path can be found here: http://msdn.microsoft.com/en-us/library/7d83bc18.aspx
In my case, being sure all needed dlls were in the same directory and doing a os.chdir() to that directory solved the problem.