1. Try changing the field property of Access DB to Unicode (If the field type is TEXT).
2. Try changing the field type of Access DB to BLOB (If it is TEXT now).
3. You may try with a different one.
4. If you have the source code for the converter then you would also try to fix it for you.
longer versions of varchars, inside phpmyadmin or mysql you can change the type of field from varchar to blob i think if i remember, i remember messing with it for storing images or files