[quote user="Jon Mercer"]Could someone either point me to a reference that I can look up these codes [/quote]
MDL errors are mostly to be found in the C header mdlerrs.h, which you'll find in the ..\mdl\include folder. SUCCESS == 0.
Where the MDL function reference manual publishes VBA declarations you have to translate those into C#. Anything that is a C pointer is called a Long in VBA, but in C# you'll need something else. This might work — I'm unsure of the String declarations...
[DllImport("stdmdlbltin.dll", CallingConvention = CallingConvention.Cdecl)]
internal static extern Int32 mdlView_saveNamed(String viewNameP, String descriptionP, String viewNameSpace, Int32 viewNum);