(Not familar with 2007, yet.)
I believe you can leave the On Error statements as is, but change your error trapping option to "Break on All Errors." Good way to fix code you didn't know was not "correct."
Code:
'For Access 2003
Application.SetOption "Error Trapping", 2
'0 = Break on all errors
'1 = Break in Class Module
'2 = Break on Unhandled errors
Another option is to use standard debugging practices of writing to a log file (or immediate window) in order to watch the flow. Keep narrowing the logging code until you find the problem.
Depending on the code you might be able to step through.