Some maintenance upgrades have been installed on the shoutbox. These upgrades should improve overall functionality of the shoutbox.
Following carlsojos's suggestion and some other concerns raised in the past, certain restrictions have been placed on shoutbox BBCode usage. The Image BBCode is now restricted to images of no more than 100 pixels in width or height. The following BBCodes have been disabled entirely: Quote, Youtube, Left, Right, Code, and Attachment. These changes affect only the shoutbox, so you can still use all those BBCodes in forum posts as normal.
Error message handling for the shoutbox has been improved again. The system was not properly dealing with error messages resulting from post parsing (mostly BBCode parsing). These error messages, although very rare, will now be displayed if encountered. All of the new BBCode restrictions can generate such error messages.
The error message closing X wasn't working correctly in Google Chrome. This has been corrected.
There have been a few issues with posts made by logged out users, so the guest posting feature has been disabled. It might return in the future, if I have time to examine certain elements of it more closely to reduce those issues.