On the surface, it sounds like you have a data related error which had to be
introduced since the last time you did the import (assuming no changes were
made to field names etc).

A real quick test you can do is export the data you're trying to import from
Access to a CSV text file and try and import that file into Outlook. If the
error occurs in the CSV file - then it's a pretty good indication that you
have a data related issue and will need to track it down to the record/field
causing the problem which is not going to be easy to do using the standard
Outlook import engine. If the error doesn't happen when importing the CSV
file - would suggest re-installing (repairing) your Outlook installation and
try importing from Access again.

Karl