Proxy not working

Hi,
I'm using PA 12.0.5 on a Win7 Enterprise x64 computer behind a very restrictive firewall. I've tried to set it up with a proxy server I have installed at home. It worked initially, I was able to download and install about 7 programs, then I started getting a "sendrequest" error. Now, I can no longer connect at all through my proxy server, but only with PA.

I've been able to connect and use my proxy using FF and PhraseExpress without issue. The CONNECT and GET commands are almost instantaneous. But when I try with PA, nothing happens. After about 30 seconds to a minute, I get the error message.

Am I doing something wrong? Do I need to do something different? What other troubleshooting steps can I take to try to isolate the issue?

Thank you very much for your help on this issue.

Regards

Éric