- Uninstalled Kindle & Kindle Import
- Deregistered this Kindle instance from the Amazon account (it may even work if this step is skipped)
- Restart TouchPad
- Reinstall Kindle and Kindle Import
- Reregister this Kindle instance
- Convert & Push the books from PC to TouchPad using Calibre
- Run Kindle Import on TouchPad to select & import these books
That should solve your problem!