This security token error (yes I read the sticky)
 

What can cause this to happen *all of a sudden one day*. My board was working perfectly without errors. My forum is not modded.

But some people complained of being logged out too quickly so I changed the cookie setting to 5000 seconds through the admin panel. I also added a few replacement variables for bad words.

Now all of a sudden we get the invalid security token error when replying* making new posts etc...

Tried cache busting* deleting cookies and the error is still happening intermittently.

If I set the cookies back to the default could this fix it? What is the default?

Thank you for any help.