You do not have your References set correctly. This is a common problem when migrating existing databases across versions of Access. Open a module in Design mode and select Tools - References. You need to have the following two references selected and available:
Visual Basic for Applications
Microsoft Access 9.0 Object Library
These contain the common "built-in" functions like Left$(), Right$(), etc.
Hope this helps! Good Luck
-Glen Kruse
EDS