Integers in a textbox

[cid]

So basically in this database there are random numbers that are some times 4 characters long and sometimes 5 characters. I tried to make a replace function like this:

Private Sub Form_Load()
On Error GoTo move_first
Do
If GIS.Value = "xxxx" Then
GIS.Value = "R00000" & GIS.Value
ElseIf GIS.Value = "xxxxx" Then
GIS.Value = "R0000" & GIS.Value
Me.Recordset.MoveNext
End If
Loop
Exit Sub
move_first:
Me.Recordset.MoveFirst
End Sub

Anyways, this just hangs the program and forces me to do a ctrl + alt + break

if anyone has any ideas, they are greatly appreciated