Restoring user data to os10.7
Migration assistant doesn't work with individual users data unless it's backed up by Time Machine AFAIK.  

If you just copied the user folder over to the other drive, you should be able to create the new user and then copy the contents of the old user folder to the new one.

It sounds like there's something wrong with the external drive.  Try using Disk Utility to scan and fix it.  If that doesn't work, post back here with details of what happened.