Usman Asar

Paul, how big are your courses?

how much resource allocation is given to your web server?

As I assist a school running IIS/MariaDB, on 2 cores vCPU 10GB RAM, and their course backups run absolutely fine.

Perry, in your previous settings the number of files to be cached is less than what Moodle version 2.7+ holds, where validate frequency in your previous settings have been quite frequent, but anything coming new to be cached will be over-written by older files, so may be a collision between those is ending up in error.

Also, have you not tried upgrading your PHP to latest of 5.6? as 5.6.3 was released back in November 2014, whilst if you see latest release of zend.opcache extension release version 7.0.5 on April 2015 with a fix particularly for moodle.

have you already applied the new file numbers to be cached as in 4000?

I have applied these settings on multiple of IIS installations with PHP 7, and no one ever showed any error despite heavy usage.

Perry, which IIS it is? also which PHP version?
you can find all the information related to OpCache in Moodle covering both Windows / Linux here

https://docs.moodle.org/29/en/OPcache

alternatively watch 2nd video here
http://blog.academictools.org/2015/12/installing-moodle-on-microsoft-windows.html

explaining use of OpCache setting up in Server 2012 R2

James, some community members did mentioned this tool showing error as in missing from disk, I think mostly that were pulled from git repository. You can simply uninstall it with no effect to moodle.

AdSense when used in HTML block works perfectly well with moodle.

have you been trying to import code from outside source?

now coming to a possibility, that would be use of mod_security in your hosting, you have to turn that off, for moodle shows up trouble with that.