A better question is if the OP scanned for codes. You really can't work on these cars without a good OBD diagnostic tool, one capable of not only scanning for fault codes but also clearing them.
It could be the ABS system, but I suspect the pad interfaces need to be lubed. A bad sensor probably won't cause brake drag, but it will cause a half dozen other codes to be thrown, and you can't clear them without a good OBD tool.
http://f30.bimmerpost.com/forums/sho...2#post23288222