Adding Classified Gives Weird Screen

[assemblytube]

When I add a classified I get a strange screen. I attach a screen grab of what it looks like.
The screen stays like this but if I edit the url in my browser and go to the classified section of the forum, the classified has been added.

Anyone seeing this screen on adding a classified would be very confused.

Any ideas on how I can prevent this happening.
Thank you.

[SMFHacks]

Never seen that happen. What mods do you have installed? I am thinking it is a mod issue.