Has nothing to do with your code... it's a problem with Microsoft's code. There is a well known bug in eVB where the left function will ONLY work in a module and not a form. You have two solutions:
Use the MID function instead of left.
-or-
Create a public function in a module call MyLeft and just wrap the left function.
Here is the knowledge base article explaining the issue:
http://support.microsoft.com/default...b;en-us;180455