But the error wasn't related to ANSI or Unicode, it was about that method from libshfolder!
When libshell32 and libshfolder are added to sdk, under Windows 98 a Unicode build of Code::Blocks shows a message box of wxWidgets "saying" it cannot run because of Unicode support under Win98. This one couldn't even appear!
If those libraries aren't moved to sdk, the next ANSI build won't run on Win98.
But... somehow... you're right about something: I forgot it wasn't an ANSI build, but anyway, the problem is still there in the project file.