Assertion failed in bartool.cpp (on VC 6.00)?

I have a big problem since I migrated an application from VC 5.00 to VC 6.00.
My application uses a toolbar class built over the Comctl32 dll, it worked well with VC 5.00, but with VC 6.00 I cannot debug it anymore. I always got assertion failed in the MFC source file: bartool.cpp.

The assertion is the following: ASSERT(_afxComCtlVersion != -1);
The Microsoft explanation did really not help me.
I had IE4 but I tried to install IE5 but have still the problem.
And of course the release version works perfectly!

Does anybody know a method to not have this bloody variable set to -1!!!

Help!!!!!!!

Jean-Hubert Morin