Getting ajax error in v155 with v154 Westminster template

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.

Just noticed than when I click the login link it immediately goes to 'Login Time Out' page, as this title is displayed in the tab for the otherwise blank page below the top wrapper.

New version of ajax.php made no difference.

Is this the thread to which you reference but didn't post? https://www.zen-cart.com/showthread.php?219801-Making-v154-DIY-Picaflor-Azul-templates-work-with-v1-5-5&p=1306879#post1306879

Apologies for that omission - no, it is this thread:

https://www.zen-cart.com/showthread.php?219766-Getting-ajax-error-in-v155-with-v154-Westminster-template&highlight=ajax+error+v155

Thanks for pointing me to the other. That is great. I think!