If all transactions are importing using the same payee name, you probably have an Import Rule that is applying this payee name to all transactions when importing. Go to View> Show Import Rules to view your list of Import Rules. Look for a rule with the Payee name or Category which is being applied to your importing transactions erroneously and deleting the existing Import Rule for this Payee name.

For more details on Import Rules you can also refer to the iBank 5 User Manual starting on page 173:  http://www.iggsoft.com/manuals/iBank_5_Manual.pdf