Your submission could not be processed because a security token was invalid

[martin2345uk]

Hi,
Not sure where to post this, sorry if completely the wrong place!
On my PC when I try to mark forums as read I get this

Your submission could not be processed because a security token was invalid.

If this occurred unexpectedly, please inform the administrator and describe the action you performed before you received this error.

Does anyone know what that means..?

 

[Peter Mugridge]

I've read about this before; I think it's something to do with a security setting being too high somewhere.