I had the problem with a completely blank WEBi login page in IE 11.
The problem is that IE cannot load binary data with ajax if it is not encoded properly, and WEBi uses ajax to load some big parts of the dojo framework asynchronously.
I "solved" it (explained at
http://serverfault.com/q/625004/50874 ) by decompressing the javascripts and css files that were gzipped, and actually got it to work in IE11 too!
Why it stopped working in IE11 is probably because Microsoft chose to change the UserAgent (removing "MSIE" from it), which makes old frameworks fail the guess-the-browser game on IE11, which in turn causes the code to miss the extra hoops that must be jumped through on microsofts browsers, since IE11 appears more like Mozilla in the user agent string.