IServiceProvider error: ambiguous symbol message

I have been working on porting code from VS2003 to VS2005. The last error message I received before being able to compile it was:

error C2872: 'IServiceProvider' : ambiguous symbol

Lucky me, this error is well documented. The solution was moving the #include to the top of the file. It works for me and I did not look further on the cause of this error. However, it seems this symbol may be declared in more than one file.

This is one area where Microsoft could follow ESRI's approach. ESRI does not declare repeated names, it adds a number to the end of the class that can be incremented, i.e. ISpatialReference, ISpatialReference2, ISpatialReference3. Note that ESRI is actually extending a class with each increment and Microsoft may not be doing that.