Need help with programming in Access 2003.

[WannabePrgmr]

I have a main form called "Master" and it is a data entry form. 5 users will be entering data at the same time for 8 hours a day Monday - Friday (not that that really matters). Basically, people call in with issues, and we log the info.

It's set up that there is an AutoNumber box that continually counts up for every new form.

I have a textbox that is a lookup box for old reference numbers. The user puts in a reference number and it brings up whatever record that is tied to that reference number. I used the following code to do this:

Dim rs As DAO.Recordset

If Not IsNull(Me.cboMoveTo) Then
'Save before move.
If Me.Dirty Then
Me.Dirty = False
End If
'Search in the clone set.
Set rs = Me.RecordsetClone
rs.FindFirst "[Reference #] = " & Me.cboMoveTo
If rs.NoMatch Then
MsgBox "Not found: filtered?"
Else
'Display the found record in the form.
Me.Bookmark = rs.Bookmark
End If
End If
Set rs = Nothing

My question is, when one user is updating a given record, I don't want any of the other users to be able to go into that record as well. So if another user types in that reference box that same number and clicks enter, it shoud bring up a message that states "This record is being updated by another user".

I have programming that works for each individual computer that will pop up a message but another user from a different computer is still able to go to the same record being updated???

Any help would be great! I'd be happy to paste the whole project if it would help diagnose a solution.

Thanks!!!!!