I provide tech support to about a dozen families and to several non-profit organizations. I encountered something today that might be helpful for others who run into the same issue.
The Ex. Dir. of one of the non-profits brought her Toshiba laptop to me, complaining that she could not access the organization’s e-mail website post installation of the Win 8.1 update (did not have the problem with Win 8). I neglected to check to make sure she had the latest version of Avast :'(, but since updates are supposed to be automatic and she uses the computer every weekday, I assume she does. She was using IE 11 as her default browser. I cleaned up the junk files and unnecessary registry entries using CCleaner, and there were a lot of them. Also updated 6 drivers using Toshiba’s notification system and Driver Booster. This did not resolve the issue.
I tried disabling Avast’s shields; did nothing. I then tried resetting IE to the factory default. After closing and reopening IE, access to the e-mail website was successful. Because the reset process disables ALL extensions, I re-enabled the Avast add-ons (only; left all others disabled). Closed and reopened IE. Would not open the e-mail website. Disabled them and the website again because accessible.
Obviously, the Avast add-on does not have this negative effect on all websites, only some. So if you encounter a problem like the one described here. try disabling the Avast add-on(s) in IE.