Drive letter in use on Windows 7

Hi.

When I connect my U3 drive to my Windows7 Ultimate system a message told me that the drive letter Launchpad will assign for my drive is already in use.

No idea what to do, there are no network shares with those drive letters assigned.

Silly thing - on my enterprise W7 desktop no such problems occur.

Does anyone has any idea where to find the point?

Thanks ion advance.

Peter

RIGHT click   on Computer, click on Manage, click on Disk Management.  What drive letters are in use?