>>>Extra info: just after I send a message the MessageBox crops up.
>>
>>What do you mean by "crops up"?
>
>Shows up...

Ok, so you mean, just after you successfully sent a message, you got that javascript error. For some kind of reason, the hidding frame which process several hidding transactions is not processing ok on that version. Have you been able to collect some info from the javascript error that could help us troubleshoot the problem? You may also proceed by email from now on in order to avoid creating more messages on that topic online.