The below code runs fine if cell B5 has changed. However, if I replace B5 in
the code below with E5, the code runs even if Range("AA5").Value = "". It
only runs once though and at the end I get an error box, "application defined
or object define error?" I can replace the below code with any cell except
E5 and it works perfectly. I've tried changing the format of cell E5 and
various other things and I still can't get it to work. Any ideas?

On Error goto ErrHandler

If Target.Address = "$B$5" And Range("AA5").Value < "" Then
Application.EnableEvents = False
Call Input_FieldsNoPartNumber
End If

ErrHandler:
Application.EnableEvent = True

End Sub