Again another golden oldie I cam across. A client was integrating their CRM plugin with Outlook 2013 (In this example it was SalesForce, however they have since notified me that all add-ins from the Microsoft store also crashed Internet Explorer).
When they opened up an email and hit the CRM button, Internet Explorer would crash with the following error:
App Crash,
Internet Explorer.exe
Faulting Module :ierutill.dll
Problem version of IE 11.9600.16428
After disabling and re-enabling various plug-ins I got the the source problem, UAC. It turns out the client disable UAC via GPO, because
As you can see from above the UAC is disabled, we set the UAC to Default and applied, upon testing the add-ins in Outlook again they all functioned correctly.