2CO Gateway "Error Message"

2CO Gateway issue- (v 2.0.7)

I've been with 2CO a few years and never had a problem adding to a store or checkout. With the Member plugin it gives an error message no matter what I do:

"There was a problem connecting to 2CO. Please try again. REF:403"

I have 5 Membership levels and all give the same error after clicking "Register My Account"

-I have re-checked my Gateway info numerous times.
-I have run the "Repair Membership" check and it shows no errors.
-This website is one of 8 on my WP Network. This is the only one with Membership

Observation: All other sites I use with 2CO ask for the same Gateway info, except they also ask for
the "product code of each subscription". I notice the WPMU Member plugin does not.

I'm baffled. Any suggestions?