I've been able to replicate the error and I'm in the process of finding a fix. When I got the error I clicked on the back button (top left) and it came up with the sign in page with all the fields filled in except the password field. Filled that in and all was normal.
Not sure what's causing it but I've seen a few posts with the same error problem. I think this happened before some months ago.
URL stands for Uniform Resource Locator. A URL is a specially-formatted string of text used by Web browsers and other network software to define a location on the web. And yes
www.diglis.com is a url.