If you get an access denied error about CREATE TEMPORARY TABLE when you search, the MySQL user assigned to your Phorum database does not have the rights to create temporary tables, which the search feature uses. To fix this, either grant your user temporary table creation permissions through a tool like phpmyadmin, or if you cannot, then contact your host to see if they can enable it for you.
If you cannnot obtain permissions to create temporary tables, you can
install the "Non-Temporary Search" module which you can find in our
online list of modules
(warning: it will be a slow search on large data sets!)