Is the Mark all forums read not working? I can't seem to mark all the forums read >.< .
I kept refreshing...cleared my cache etc.
Works fine for me when I hit the link on my end.
You said you tried to clear your cache, always the first step.
Did you restart the browser as well?
Stupid question, but if you are using IE or it's clones you need to.
Firefox you may have to depending on the session cookies and all that fun stuff.
I'm using firefox.
Mine is just a "no plugin" only just a custom skin. It USED to work.
It works fine with me. I'm using Opera browser.
I guess it is your browser problem.