To check the free space: Open <My Computer>, right-click the drive in question, select <Properties>. It will tell you there.
Also, check your permissions again. You need to make sure that you have <read and write> permission for the drive where you import photos to and for your user account.
Also, you need <read and write> permission for the drive where the Lr catalog resides.
With Lr you need <read and write> permission for every drive that Lr is using in some way.
