Is it possible you have can view thread contents set to off for guests?
Also, do you have vBO integration on? If so, you could try turning it off.
If all of that fails, then feel free to throw me a PM with FTP / AdminCP with Can Admin Plugins and Can Admin Styles and I shall get to the bottom of it
This has now been solved, the problem was that InfoPanels incorrectly required "Can Search Forum" permissions as well as "Can View Threads", which has now been hotfixed on your site and the release package was updated
Thanks for your help in identifying this, literally couldn't have done it without you!