Hello. I got the same problem with an 5.15 Xpression version. I can drag and drop materials but when I try to import them from the material manager the application shut down.
I checked the "Control Panel > Administrator Tools > Local Security Policy > Local Policies > Security Options > User Account Control: Run all administrators in Admin Approval Mode" and he's "Disabled"
This application use to work great and nothing changed in the configuration lately.
Best regards
Florent
#XPression