Access Missing Data

Hi I built a small data base from a MS template, added a few extra fields nothing complex. imported data about 10,000 contacts and then recorded call records which were linked to the contacts table. All worked fine until i placed it on our server and gave two people access to it. it seems data is just not saving for great chunks of time, then miraculously it starts saving again.
Is this something others have seen?
Is there some sort of permission that should have been ticked be fore two people in a work group used the same data base??
thanks in advance
Tim