I can't tell you anything else than to do exactly what I told you.

But here's again for good measure:
When the installers of both EB 1.1 and EB 1.2 ask where you want to install it, put the following in:
"E:\my games\D&D"
Nothing else but that. No E:\my games\D&D\EB1.1, no subfolders, just "E:\my games\D&D". Do that and it will work, install 1.1 and 1.2 to different folders and it won't work. Just try it.