"I went into Internet Options, selected the Content tab and clicked on the Clear SSL State button"

Fantastic. I started to get this error (out of the blue) a couple of days ago when trying to connect to work. The Citrix techies advised I try a few different things but nothing made any difference. For a complete not technical muppet like myself its a bit scary clicking on a button that says "Clear SSL State" without having a clue what it will do but out of desperation I tried it and it has worked perfectly. I have no idea if I have caused problems elsewhere with my PC but at least I can connect to work again. Many thanks for the advice.

>> Protocol Driver Error workaround