Shared DB

can anybody tell me why my colleague cannot add records to a DB I set up on my pc.

i have a DB with 3 tables linked (all one-to-one).

i can add records into it fine on my pc but when my colleague tries on her pc it allows her to enter data but when it comes to moving onto the next record it wont allow her to save the record.

To explain further. there are 3 tables as mentioned before. lets call them Table 1, Table 2 and Table 3. When my colleague uses the form to add a record it wont let her save it as it says a related record is needed in table 2.

any ideas why it works perfectly on mine but not on hers?