Go back into the EPST settings, go to security tab, & check your user name & password. They must jive with your carrier specific requirements. For example, my HDR user ID would be
5554441212@alltel.net, and the HDR password is my esn number. the PPP user ID is once again
5554441212@alltel.net, and the PPP password is alltel. See if this helps, if not you may have to flash back to your stock rom and start all over.