Getting ajax error in v155 with v154 Westminster template

[godt]

There is a recent thread with this title which is closed. I need to reopen it:

Quoting Dr Byte from the old thread:

"Re: Getting ajax error in v155
As I said earlier, the Westminster template replaces some core v155 files with older versions.
Two of note are:
/includes/templates/YOUR_TEMPLATE_FOLDER/jscript/jscript_framework.php
/includes/classes/Mobile_Detect.php

And maybe others. Copy the v155 versions of those files back in, and see what happens."

I have copied the 155 versions of these files into their respective places, but this has not solved the problem. How can I begin to know what other files I might replace?

The only difference made by copying the 155 files over is that the error no longer displays. No site page loads at all.