Hello, and welcome to the forums!
God, that problem sounds ugly. Kudos to you for modifying the browser "User Agent" (UA), but I'm afraid that you've run into a computing-neighborhood bully known as Micro$oft which neither works nor plays well with others. IMHO, the only admirable thing they've ever done were the ODBC drivers.
I'll bet money that a proprietary scripting language known as "Active-X" is needed on the page you're trying to display, and I haven't yet found any Android support for it.
It might be out there somewhere, but I'd rather be hunting dog-doo with a pointed stick than try to work with the M$ bully. Open-source web tools such as Apache, MySQL and PHP are freely available and work so much more reliably than any M$ crap.
Suggest to your employer to get a real operating system and tools instead of that home-handyman garbage. ;-) The webserver, database and scripting language mentioned above will even run on the M$ OS, as an example of others who are willing to work and play well even with the bully.