Ok, I have split an Access mdb into a FE and BE. The updates work and inserts work fine on the server machine. However, when the workstations try to update and insert, they show success on the local??? copy of the db but nothing affects the totals on the master copy at the server.
Are your tables in the FE database linked to the correct back end database?
Go to Tools -> Database Utilities -> Linked Table Manager to verify where your tables are linked to. They should be linked to the back end database which is on the server. Do not use your mapped letter drive to link them(use the whole path of the server) to make sure that all users will be accessing the correct database.
"...I have split an Access mdb into a FE and BE...."
after you split, there should NOT be a local BE to get itself updated. the BE should be on the server and should be the only active copy of the data.
your clients should only have the FE, and should link to the BE on the server.
try an experiment on one of the unlucky clients. install the FE and manually link (File¦External Data¦Link.....) to the BE. once that works as planned, you either tell your other clients how to manually link (it's a one-time setup thing, and far from rocket science) or you code the FE to link automatically (beware variations in the server drive name amongst clients as klarat says).