If you get a red x with no attachment info, that means that creating the db table failed and you might have to do it manually.
A few people have reported this, I may need to update the plugin.
Please try downloading a new copy of the plugin (remember to copy over your settings) and DEACTIVATE the plugin, and then REACTIVATE it again.
http://plugins-svn.bbpress.org/bb-attachments/trunk/bb-attachments.php
The reactivation should cause the db table to be created and the errors to go away.