I get an error connecting to MS SQL Server from my php script on windows

Connecting a php script to MS SQL is certainly doable, but some server settings might block you. 

Here's an error I was getting:

Failed to connect to database
Login failed for user 'IIS APPPOOL\DefaultAppPool'

The solution in this case was to update the file:

C:\PHP
\ntwdblib.dll

In the classic Windows way, that updated dll fixed the whole error like magic.