Modules & VBA :: Error Message On Creating Duplicate Record

I need to be able to produce an error on a form where the user attempts to create a new user that already exists. The error needs to be produced when the save button is clicked.

See below for the existing code on my save button which exists in form, 'frmAddEditUser':

Private Sub cmdSave_Click()
If IsNull(cboManagerID) = True Then
MsgBox "Please select a manager", vbExclamation, "Details Missing!"
Me.cboManagerID.Requery

[Code] ....

Currently, if I attempt to create a user with the same Payroll ID as an existing user, my 'User details saved' message box is displayed and to the user it looks like a new record has saved successfully which isn't the case.

I need a message box to appear displaying something like "Payroll ID n already exists" where n is the 'PayrollID' of the duplicate record. (Is it possible to combine a value from a certain control and ones own custom text?)

Note: PayrollID is a combination of letters and numbers, i.e. two letters, followed by 5 numbers, e.g. JD12345.

For reference, the table/field and and control are called, '[tblUser].[PayrollID]' and 'txtPayrollID' (on 'frmAddEditUser') respectively; it is from this field and control that I want the error to be produced if the user is entering the same values which are existing in 'tblUser'.