Google shows
several interesting results.
The general consensus is that the database table "usertextfield" does not exist, or is not accessable. Bad forum backups and restores can have this effect.
Alternatively, the MySQL user in your config file does not have the appropriate read/write privilages to the table. This is generally an error with the users table in MySQL's settings which can result as either a bad move from one server to the other, or a bad sector on the server's hard drive.