What version of Desktop Manager are you using? If you're using DM 5, you could try uninstalling it and getting 4.7. Be sure to temporarily turn off real time protection on your AV while installing it.
Also is this on XP or Vista?
Another possible problem is drive letter names. There are some posts here about that, should come up on a search.
Edit...maybe not your problem, but worth checking.
http://www.blackberryforums.com/gene...rd-via-pc.html