Is Plesk 8.4 compatible with PHP 5.2.6 and MySQL 5.0.58? Options

[ling]

Hi I'm very inexperience with servers and control panel. But our company has just migrated to an unmanaged server with PLESK 8.4 control panel. We upgraded PHP to PHP 5.2.6 and MySQL to MySQL 5.0.58 based on the advise of our programmer. Before that our webhost warned us that the old version of PHP & MySQL are bundled with PLESK so if we upgrade them separately... some disruptions or errors may occur.

Now we are experiencing some email disorders:
- webmail doesn't work - error msg on screen says,"A fatal error has occurred. DB Error: extension not found. Details have been logged for the administrator."
- Sender received failure msg, but we received the mail

Are disorders cause by the upgrading? Anyone can advise if the upgraded PHP & MySQL compatible with PLESK 8.4? If not, what sort of errors will likely to occur? Much appreciated.