Opening acsm wants to uninstall digital editions!!!

Hi, peoples!

At my computer I have no problem opening acsm-files via Digital Editions, but if my wife tries the same at her computer (Windows 8.1), when she tries "open with default program" and she clicks on ADE, she gets a little window in which she can only choose "uninstall ADE" or "Cancel". Tottally rediculous!!!

Can anybody please help us out?!!!   Already tried to unauthorize and authorize several times, uninstall and install ADE again, but to no avail...

Thanx in @dvance