Hello-
I have experienced this problem once before and Themeco Support was able to fix. I do appreciate your help in advance.
Eric
Hi There,
Thank you for writing in, I saw a 406 error code when I tried to save your page, most of the time (but not limited to) this issue is related to security. Please contact your hosting on how to disable the mod_security rules, or exclude all X/Cornerstone assets from the mod_security ruleset (show them the screenshots below and they may find something about it).
Also while we are on this, please deactivate all your security plugins (WordFence, etc) and any caching feature your site might have. This is to make sure that all changes we made is taking effect immediately.
Also check the file permissions on your site (https://codex.wordpress.org/Changing_File_Permissions), as we are getting an invalid_user error.
You can also do a testing for a plugin conflict, as it can be also possible that its a plugin that is being blocked and not the Cornerstone. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it’s fixed, you’ll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
Let us know how it goes,
Cheers!