Debugging _CheckNotSysLevel() errors?

[Dan Kegel]

http://bugs.winehq.org/show_bug.cgi?id=4063 is a crash
on exit from a VB6 app due to a _CheckNotSysLevel() error.
What typically causes these - are they a bug in the windows
program?  And is there a good reference from understanding
the whole syslevel thing in gdi?
Thanks!