What kind of problems are you running into? Make sure that you double check the C signature in the generated .h file. I've seen people run into problems with the cdecl vs. stdcall issue.
Example-wise, any Dllimport example will work because from the outside, the DLL looks like a C DLL.
Also, where is your C# code running? For example, there are issues with ASP.NET and LV DLLs (see my blog for details).