To anyone having problems with the modify button not working (loading the same page or not being able to check out) try another browser. I had the same problem using Chrome but switching to either Firefox or Opera I had no problem.
Thanks for your suggestions. I have tried multiple devices and multiple browsers without any luck. Guessing it has something to do with their system and/or the reservation itself. I read somewhere that MM can mess it up and I do have MM so maybe that is it... who knows...