Security Ticket Missing or Unmatched?
 

Your submission could not be processed because a security token was missing or mismatched.

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

Where are you getting this error? If in a custom form, add this field:

I get it every time I try to post.

This thread talks about it and how to fix it - Implementing CSRF Protection in modifications

Where do I put those codes? What files? It is unclear

Please ensure you have reverted all your templates, if this does not solve your issue create a New Style with no Parent Style and test the functionality again.

Do you have a downgrade to 3.6.8?

No, as I mentioned in my previous post, you need to revert any customised templates which are out of date. (The should be listed on the AdminCP index page).

If there are none there, create a New Style (AdminCP > Styles & Templates > Style Manager > Add New Style) with no Parent Style and test to see if the error occurs in this skin.

i never find that error on my forums but i get that email about

Missing or Invalid Security Token detected.

That might be a false positive. I have been getting a couple of them every now and then on default vb files.