Tmobile Prism 2.3.6, web2go, server error and no plan change

I have a Tmobile Prism OS 2.3.6 and get the 'Server error' when attempting to change plans. I have the Prepaid plan and have always been able to do this on the G1 phone. I can of course change the plan on thru the web but not web2go. I can make the system think it is changed using the web, but the new plan still doesn't work on the phone. Have removed webguard.

Thanks!