Merton,
People dont know much about solving DWA-140 problems and moderators / dlink staff doesnt show up here a lot.
The best advice i can give you is to try google or a Mac specific problem.
As you can see, there are a lot of unfinished threads at this forum, regarding Windows 7 and MAC.
Ive got a DWA-140 and my conclusion is that its a good USB adapter with serious unsolved problems with some OS.