It is possible that this user was assigned a teacher role in some context. As a consequence, this users will get the most restricted permissions fot the assigned roles in a given context.
I leave here some options to help solve your problem:
- others with the same problem in forum - http://moodle.org/mod/forum/discuss.php?d=66281
- in case it is a corrupted database, check this - http://docs.moodle.org/en/Administration_FAQ#How_do_I_repair_a_corrupted_Moodle_database.3F
- script to reset permission, must be used with care (read the help file) - http://cvs.moodle.org/contrib/tools/adminfix/