/webassist/framework/ajax_wrapper.php error on checkout page all of the sudden on multiple sites...

I tried several threads but to no avail. This has popped up on two different sites (built in tandem mirroring each other closely) at the same time. They are at least three year old sites that haven't had significant work for several years. Made some changes two months ago, but nothing to do with the cart. Client just notified me this AM both sites now throw the following error when trying to 'continue' on the checkout page:

"Not Acceptable
An appropriate representation of the requested resource /webassist/framework/ajax_wrapper.php could not be found on this server.
Additionally, a 406 Not Acceptable error was encountered while trying to use an ErrorDocument to handle the request."

I've confirmed all the /framework/ pages are mirroring what I have locally. I've re-uploaded the ajax_wrapper.php in case there was some sort of a file corruption issue. I've tried to confirm file path though it looks like it pulls from the JS file that gets me a bit lost. It's odd because nothing in that folder has been changed.

Could some sort of server software upgrade throw a wrench in the ecart system from a few years ago? How else can I troubleshoot?

framework folder and checkout page attached.