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1. it's in init_sanitize.php because at that point in time that was the best location for doing that particular sanity check (which has mostly the same letters as 'sanitize')
2. outside of this USU...

@carlwhat, you can probably accomplish the same thing in the original line, by simply adding an extra set of parentheses around:

($cID !== null ? $cID : $result->fields['master_id'])

(ie:...

It doesn't.
You must have given that /mobile/ URL to Google via a sitemap or a link from another site, or something else.

Here's a really simple way:

a) visit a product in your store
b) note the URL
c) see the pattern: the segments with slashes etc, and where the product-id number appears

Now you can replicate...

There is no "override" for the /includes/classes folder. Alterations to files in that folder must be made directly.

Probably need to also fix whatever is rewriting things to point to invalid locations. And maybe turn back on the Missing Page Check setting in Admin->Config->My Store.

When Apple-products try to surf around your site, instead of looking for favicon.ico files first, they look for apple-touch-icon.png files.
If you create that file, then this specific issue will go...

The error message you're getting is caused by your plugin trying to do stuff with v1.5.x tables when they don't exist.
So, if you're really upgrading only to v1.3.9h, then I'm guessing you grabbed...