For what it's worth, here are the plugins I am running, most of which are native to the WP build:
MCE Table Buttons
Platinum SEO Pack
Public Post Preview
Tiny MCE Advanced
Wordpress Editorial Calendar
I've tried disabling each one individually to see if the checkout button becomes available but no effect.
The thing that stinks here is that I have like 15 people trying to sign up but cannot because of this. So, time is money here. Please respond ASAP...tks.