Can you clarify which GWT version and which IE version you are using? Thomas is right of course that the next GWT version won't even be able to start legacy dev mode, and other recent releases have removed specific implementations of UI types that needed IE specialization - but if you use GWT 2.10.1 IE11 should still work, and GWT 2.9 will support IE 8-10.
With that said, the icon and buttons in that error message don't look to me like IE, but chromium - and that error message appears to be a chromium message format. Indeed, here's the constant value in the chromium sources:
Can you confirm that you're running IE11 or earlier, and not Edge?