Updated to iTunes 12.1, now iTunes crashes every time it attempts to access the internet through our internal proxy - cannot access store!

Question

Hi,
Does anybody have any experience of using iTunes with a web filtering proxy? My home is using the Sophos UTM home edition to provide edge antivirus and content filtering. More information available here: http://www.sophos.com/en-us/products/free-tools/sophos-utm-home-edition.aspx
The proxy settings for the computer is set to use an automatic configuration script "WPAD" and the settings are locked by group policy and cannot be disabled or changed.
Now here's the problem, when launching iTunes, the iTunes prompts me to enter login details for the HTTPS proxy. That's all well and good, so I enter the login details and hit okay. But when I go to the store tab, iTunes crashes with javascriptcore.dll. This makes sense because a WPAD proxy configuration file is pretty much JavaScript code. But this should not happen, as now I cannot access the iTunes store.
Prior to iTunes 12.1, iTunes would sometimes freeze when attempting to access the store but it would eventually work.
The proxy logs are not showing that any iTunes requests were blocked, dropped or otherwise rejected.
Does anybody have any suggestions to get this to work again or at least work around the issue?
NOTE: Disabling the proxy is not an option because the proxy settings on the Windows computers are locked through group policy. I can however, edit the WPAD proxy configuration file and add exceptions to the proxy but I don't know where to start!
I will also post this on the Sophos UTM support forums.
Thanks in advance.

Answer 1

For general advice see Troubleshooting issues with iTunes for Windows updates.
The steps in the second box are a guide to removing everything related to iTunes and then rebuilding it which is often a good starting point unless the symptoms indicate a more specific approach. Review the other boxes and the list of support documents further down the page in case one of them applies.
Your library should be unaffected by these steps but there is backup and recovery advice elsewhere in the user tip.
If the advice above doesn't resolve things you could try this alternate version:
iTunes 12.1.0.71 for Windows (64-bit - for older video cards) - itunes64setup.exe (2015-01-28)
Or roll back to the previous build:
iTunes 12.0.1.26 for Windows (32-bit) - iTunesSetup.exe (2014-10-16)
iTunes 12.0.1.26 for Windows (64-bit) - iTunes64Setup.exe (2014-10-16)
tt2