So we have just started experiencing problems with web apps through Portal for ArcGIS 10.5.1 where the header controller widget is failing to load. The error I am seeing is:
create [themes/FoldableTheme/widgets/HeaderController/Widget] error:Error: Access is denied.
This is only happening on IE, on Firefox it works fine. Has anyone else experienced this problem? I've also noticed that this problem is possibly related to a specific build of IE (11.0.9600.19266), we have tried on a couple of other versions of IE (notably 1.0.9600.19236) and this problem does not occur.