Recently I was working with one of the developer who earlier designed an CDOSYS based mail component in his C++ application built using earlier Visual Studio (2005) version . After migration to VS 2008 environment, they noticed compile errors with the same code/no changes made. When I debugged further and noticed that the msado15.tlh and cdosys.tlh are not generated correctly for some reasons. When I compared the .tlh file generated by previous VS version, i noticed differences in it – as couple of keywords are missing in method definitions in the .tlh file generated by VS previous versions. That’s the reason, they noticed the compile time/linker errors.