Same problem here. I run a Joomla 1.0.x, PHP5/MySQL5.
With Firefox 3.0.2, the submit buttonn does not submit, but displays a kind of reload/refresh icon for a half second (icon with 2 arrows, something like that).
With IE7, hitting submit opens an error window with the text "Request failed" and it replaces the text in the body field with an error which seems to point at the SMF Forum (which I run in briged mode). Prolly the error is related to that. As the User/Login Component, I use CB (and have activated that in the JoomlaComment Config).
The message that is put into the body input field when hitting submit in IE:
<br />
<b>Warning</b>: require_once(../forum/SSI.php) [<a href='function.require-once'>function.require-once</a>]: failed to open stream: No such file or directory in <b><mydomain>/mambots/system/SMF_header_include.php</b> on line <b>67</b><br />
<br />
<b>Fatal error</b>: require_once() [<a href='function.require'>function.require</a>]: Failed opening required '../forum/SSI.php' (include_path='.:/usr/share/php:..') in <b><mydomain>/mambots/system/SMF_header_include.php</b> on line <b>67</b><br />
The URL to my site:
www.igs-corp.net