An excerpt from the MySQL documentation.
"One problem in MySQL versions before 3.23.2 is that if a HEAP table exceeds the size of tmp_table_size, you get the error The table tbl_name is full. In newer versions this is handled by automatically changing the in-memory (HEAP) table to a disk-based (MyISAM) table as necessary. To work around this problem, you can increase the temporary table size by setting the tmp_table_size option to mysqld, or by setting the SQL option SQL_BIG_TABLES in the client program."
There is a fix for thise using some sort of SET command with MySQL but I don't know enough about this to advise you on it, thou from this part of the documentation I can guess that if you upgrade MySQL to the latest version then it should solve your problem.