Server 2012 R2 Domain picking up wrong proxy setting

I'm trying to resolve an inherited issue involving users picking up an incorrect Internet proxy setting. The Domain is in a school and it was initially set up in NT by an external IT Support Company who subsequently migrated it to Server 2003. In setting the Domain up they used script files and registry change files. In my time the 2003 box was migrated to Server 2008 and more recently to Server 2012. In the 2008 days there were occasions when IE was picking up a proxy setting that the initial installing company had used at another school where they looked after IT. This seemed to affect just staff but as it's the case that on Student logons the Connection tab of IE is greyed out I can't verify if it's a Domain wide issue.

Post the 2012 migration; we had to make it a migration because of things like the School Information Management System that runs on the Domain, this issue is now hitting with a vengeance. We have searched all the registry entries, BAT files and GPOs but all seem to be set to the correct sslfilter.proxy... yet the wrong proxy setting keeps getting populated. Any suggestions on how to track this particular gremlin down would be extremely welcome.

 

Thanks @TonyT - just wish I could find it and alter it. I have searched high and low to no avail. I wonder where it could be hiding?

 

I'd love to mark this thread as solved but sadly at present it isn't. Oddly the old proxy setting is getting picked up from somewhere quite randomly. Some log ons get the right proxy but others persistently get the old one.

 

Thanks @Tony_T I'm hopeful that this issue might, just might now be resolved. Following input from the Euugeek.net/forum checking the Group Policy settings I found that the proxy had been set correctly but the boa for it was indicating red. Pressing F5 turned it green. As this is a school issue and the school is on holiday this week coming I haven't had a chance to test if that has solved it yet. Your suggestion was most welcome but alas I was finding that the proxy was reverting after each restart with even my Admn logon on the DC!