Error with forum Modul 5.1

Hi,
when i want to publish an new Thread in an fresh Forum as anonymous i get this error.
See Screenshot Forum-error.png

You can test it here. http://new2.lundp.de .

After error happens and we go again to the site the thread is there.
But inside you can see that there is no Avatar for anonymous. Maybee an Default Avator for this Kind of users are welcome :) 

PS: The Editor works really bad under IE 10. With every edit i got white lines inside.