Hi,
This problem was discussed here before and now I have exact the same issue. It happened after replacing the battery. Radio unit on most WV will not work after battery was disconnected as a part of security feature. But in my case VW Bettle 1999 - it still works, just Bass/ Treble won't adjust in Radio mode and Bass/Treble/Balance won't adjust in CD mode. I think it could be some sort of security issue as well. I was reading a lot on VW forums that offers some hidden key combination that some people tried to recover their units from safe mode, but they didn't work for me. If someone had the same issue, please share you experience. Any help will be appreciated.
Best regards, Beetle