I ran into this problem: I tried to view the list of recordings and nothing happened.

The error message from "tail /var/log/apache2/error.log" was the following,

[Mon Aug 23 11:53:09 2010] [error] [client 194.25.15.12] PHP Fatal error:  Allowed memory size of 67108864 bytes exhausted (tried to allocate 82 bytes) in /usr/share/mythtv/mythweb/modules/tv/recorded.

To increase the memory limit I used to edit php.ini, but it seams those are only the global values. For mythbuntu you will find the file needing editing here:

/etc/apache2/sites-available/mythweb.conf

Search for the term php_value memory_limit and change it to something bigger. I use 1024M as I have lots of RAM and just don’t want to bother with it again.