Upgraded to 4.2.2 now I have a white page for a forum

[tbworld]

For education reasons you should google : "php allowed memory size exhausted". This is typically set in your php.ini. file, in-which can be raised if your host gives you access to it.

It can also mean you have a memory leak in one of the MODS you are running.

See ... "memory_limit = `128M"
see ... "ini_set('memory_limit','128M');"

http://php.net/manual/en/ini.core.php

I have seen this occur when users have many styles. Do a little research before you play with these numbers.