Ok i've had this UI for awhile now, and i've just gone to create an alt and it wont let me install the UI. When i click the install button it does nothing other than create a spam chat channel.
I've not changed anything with the UI files or anything, and it still works fine on my other characters, but i can't install it on any alts.
You'll have better luck posting in their support forum for this sort of thing, though if you're having a problem installing it on alts, first make sure that all the addons for that characters specifically are turned on / using out-of-date addons. Otherwise just re-download the base folder and re-apply them.