I am submitting my taxes for E-Filing & get a message that Employer ID is invalid for E-Filing. It is in the proper format & is also the same number used for E-Filing of last year's returns
The Employer ID is on your W-2, right? Did you import your W-2 automatically or entered it manually?
If you imported your W-2, I would get a copy of the W-2, delete it from the TurboTax return, and re-enter it manually. The import process occasionally introduces spurious data and adding the form manually takes care of this. In fact, if you don't remember how you did the W-2, just re-enter it manually anyway.
If nothing works, then you can always print and mail your return, since printed returns don't go through the same rejection filters as e-filed returns.