This is a problem that a developer sent me by e-mail and after reproducing it I have documented it here:
BUG: COMException getting DocComment of method of generic base class
http://www.mztools.com/articles/2011/MZ2011009.aspx
and I have opened a bug report at Microsoft Connect:
COMException getting DocComment for method in generic base class in C#
https://connect.microsoft.com/VisualStudio/feedback/details/683116/comexception-getting-doccomment-for-method-in-generic-base-class-in-c