vbulletin error message

[Baxter]

Mild annoyance but whenever I try to use the mark forums as read option I get this 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.

Anyone got any idea how I can fix my security tokens whatever they are?

[Flying Helmut]

I've had this message for YEARS!

I 'surf' the Forum by reading each and every thread which interests me on the "Today's posts" feed, then, when finished, I log out.

When I log back in, ALL the previous threads will be marked as "read" (or, at least, not marked as "unread").