Thank you very much for your answer. I downloaded and installed the moodle 2.2 beta, When I completed the settings and tried to do role assignment, I got the following error. I believe it is a code error.
"<?xml version=\"1.0\" encoding=\"UTF-8\" ?>\n<EXCEPTION class=\"coding_exception\">\n<MESSAGE>Coding error detected, it must be fixed by a programmer: PHP catchable fatal error</MESSAGE>\n<DEBUGINFO>Argument 1 passed to external_api::clean_returnvalue() must be an instance of external_description, null given, called in /Applications/MAMP/htdocs/moodle22/webservice/rest/locallib.php on line 88 and defined</DEBUGINFO>\n</EXCEPTION>\n"
I tried to assign a student role(5) to the user at the system level(1). I have changed the student role to a system level role already.