Drupal messages won't disappear I don't understand why, but my Drupal messages won't disappear, they just get "added" to each other. Someone has posted a similar problem on drupal.org: "warning/error messages won't disappear", but no solution has been posted yet. There's another one which is almost the same: Drupal messages won't go away.

Here's an example of the problem: 

I do have the Administration menu installed, but the problem didn't occur earlier, so I don't think this is the source of the problem.
I've already cleared cache, ran update.php, ran cron, so I'm out of ideas.

I recently installed Ubercart module, but I don't know if it has anything to do with my problem.
But there's another one which I also don't understand: if I try to open a page which doesn't exist, I don't just get a "Page not found" error, but many MySQL errors too, which looks like this: (1) (2). It's really unhealthy too... Maybe there's a connection between these problems.

Any ideas?

Thanks!
Messages are kept in the user's session, which by default is stored in a database table called 'sessions'. If your database server dies partway through the page request, the messages may not get cleared from the session.

You can see the MySQL server failing when updating the sessions table in this image due to a max_allowed_packet error.

1M is a very small max_allowed_packet for a Drupal installation. You may need to ask your host to increase this limit. Alternatively, you could turn off dblog and use syslog instead, which sends your Drupal logs to a system daemon - but this may require your host to set up a syslog location for you. 

There may be a module that implements hook_watchdog() that can save logs to a standard file. I can't find one, but if one exists, that could be a good option in your situation too.