I did a search first and that came up, but most of the supposed solutions were cleaning cookies & cache from the browser. I do that automatically when I close the browser as I have done for well over 15 years. The other solutions were fare more complicated and seemed to be directed at specific systems or circumstances.

Winy sp1 (no updates purposely)
Opera Classic v12.18
Firefox v53 Portable,
Spectrum Cable Internet (if that matters)
NO firewall or filters either in the router or software
Only one site is affected, my banks account login page. Other pages on their site are fine, only the login page; https://onlinebanking.mtb.com/

Now the kicker is, there is also a problem using Firefox, but I can login, but the "accounts" summary page didn't show the separate accounts as it should. I had to navigate off that specific page, then return for that missing portion of the page to display.

Now, what I did was to scan using Spybot (of course), CCleaner, HyjackThis, Kaspersky AVZ Toolkit, AVG & Panda. Other than some known false positives, nothing turned up other than some crap CCleaner & Spybot cleaned up but nothing suspecious.

Anyway, the special message on a blank page (I can't even get to the login page) is below;
The requested URL was rejected. If you experience issues browsing to this webpage please call the Online & Mobile Banking help line at 1-800-790-9130 and provide the Error Code below.

Your Error Code is: 6531125852694242027