When trying to run the UC4 WebInterface under Internet Explorer 11, this error message displays : "browser not compatible".
The UC4 WebInterface is not being developed nor maintained, though it's still officially supported. Thus it's not compatible with this browser.
Offer the customer to switch to the Enterprise Control Center. It is a good alternative for him, as it's a free and more recent software.
You can find all the details relative to the software versions in the Download Center.