I was also getting this message constantly for over 2 weeks, and refused to having to install everything. I have iTunes 9.2.1 on Windows XP,and iPhone 4 iwth iOS 4. I did a whole bunch of stuff to fix this, so don't really know which one specifically helped, but here they are:
1) Uninstalled MobileMe Control from Add/Remove Programs. Downloaded it and installed it again.
2) Renamed every single DLL in the directory C:\Program Files\Common Files\Apple\Mobile Device Support\bin. Every single one, gone.
3) Went to Add/Remove Programs and Repaired (not remove, but repaired) every single Apple program, including Mobile Device Support, Apple Support, and iTunes.
4) Rebooted and iTunes started working again.
Oddly, the DLLs I renamed in the Mobile Device Support\bin remained renamed. I would think that the repair would have copied them over again. But no. They are not there anymore, and everything still works.
Hope this helps someone.
Started receiving this error ever since I updated iTunes to 9.1.079.
Havn't been able to sync my itouch since. Please Help.