I wanted to be 100% sure so I downloaded the official Microsoft Windows 7 / IE 11 virtual machine instance from
Microsoft's Developer Technologies site. I then used a freshly installed Joomla! 3.6.0 site running on PHP 5.6.10 where I installed Admin Tools 4.0.0 stable.
It appears that IE11 does not support a Javascript construct that's existed for the better part of a decade. This piece of Javascript code has been present in Admin Tools 3.8.6 as well and I do receive the same error there too. I am not sure why Admin Tools 3.8.6 works on IE11 on your site because it really shouldn't.
I guess nobody reported it this far because IE11 is an end of life browser. I recommend using a modern browser like Edge, Chrome, Firefox, or Opera.
Nicholas K. Dionysopoulos
Lead Developer and Director
π¬π·Greek: native π¬π§English: excellent π«π·French: basic β’ π My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!