Hello again ;)

Some messages are not stored in the database. The only way to find out, if messages were sent is, to press F5 from time to time or reload the messenger in another way.

I think there might be a performance problem with the database, because on my testsite this problem occures in about 5% of all messages, and on my "production-site" with about 10 users online it happens in nearly 30% of all posts.

Is it possible to implement an (perhaps optional) verify-mechanism that tries to resend a message until a timeout? If sending finally fails an error message could tell the user, his message wasn't sent.

I use Joomla 1.5.22 with CB 1.4 and Standard-Joomla-Freichat-Driver

yes I too have seen that happen in very slow servers.
The verify mechanism which you mentioned is just too resource hungry and not practical.
The problem is not due to performance, it is due to the priority system in FreiChatX.
Some requests have higher priority than the other, which may lead to holding/cancellation of the current request when some higher priority request is performed.
We are trying to fine tune this system so that the request for sending messages has the highest priority.

Is there any way to minimize this? Perhaps with the timing values in the admin-backend?

Or is it possible to put the freichat-tables in a separate SQL-DB. There are more than one Ajax-driven SQL-Querys on my site, so the collision might be caused by uddeim or any other component.

The best thing now to try is installing FreiChatX 6.0
because we have solved two bugs related to your problem