RoundCube can only open emails from local users

[ahuacatlan]

RoundCube can read emails from other local users, but whenever I try to open a message from an external sender, I get:

Warning: include_once(DOMDocument.php) [function.include-once]: failed to open stream: No such file or directory in /home/vmail/public_html/program/include/iniset.php on line 93

Warning: include_once() [function.include]: Failed opening 'DOMDocument.php' for inclusion (include_path='/home/vmail/public_html/:/home/vmail/public_html/program:/home/vmail/public_html/program/lib:/home/vmail/public_html/program/include:.:/usr/share/php5:/usr/share/php') in /home/vmail/public_html/program/include/iniset.php on line 93

Fatal error: Class 'DOMDocument' not found in /home/vmail/public_html/program/lib/washtml.php on line 235

And a message at the top saying the operation timed out.

Any ideas? What logs might I look at?
Thanks

[ahuacatlan]

thanks for the tremendous lack of help!

I just asked a friend and he immediately identified this as an issue with my PHP install, since my install didn't have built in support for DOM xml.

It turns out these errors were only coming up on HTML emails, which happened to be all of the emails from users external to this server.