VIRL fails to validate salt with Proxy error and how to 'potentially' fix it
Every year I get this product and every year I have issues that cause me to give up. VIRL 1.5.145 salt errors, proxy timeouts and frustrations.
I gave this error more than enough time. In the end I used a workaround to get rid of the error so I can start studying. My approach may or may not work for you. It seemed to be a connectivity issue to one or more salt servers. By removing the 'bad' servers from the list you can get it to validate and go on your way.
The fix is listed in the comments below. Good luck with your studies.