I installed ADE 4.0.3 under Windows 8.1 and it works. I believe that according to the Windows Compatibility-center ADE 2, 3 and 4 are compatible with W 8.1.
There are, however, some bugs in ADE 4.0.3 under W 8.1:
1. Say you've got several applications open, including ADE. As soon as you switch from any application to the Windows Desktop, ADE 4.0.3 suffers an "unknown error" and it's shut down.
2. If you minimize the ADE window, ADE suffers an "unknown error" also and, again, it's shut down.
But for these 2 bugs, it seems to work fine. I cannot say anything about the other ADE-versions because I haven't tried them with W 8.1.
Thanks for the speedy response.