Error message "Mark all forums read"

[duc888]

Dear all,

one simple question. If i want to use the button "mark all forums read" I get the following message....
"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."

I sent a PM to an administrator but never received an answer.
Could anyone tell me what I am doing wrong?
Thank you.