Delete the old folder completely, unzip the UI, rename the folder that unzips, open the folder (the UI is in a folder inside a folder) copy the folder inside, to the uifiles folder for eq, then try to load.
so initially your file path is going to be:
C:\Program Files\Sony\EverQuest\uifiles\Freq_di28889\Freq_di28889
the ui files need to be in the first folder not the second one, so change the first folders name like this:
C:\Program Files\Sony\EverQuest\uifiles\Freq_di28889a\Freq_di28889
Now copy Freq_di28889 from inside Freq_di28889a to the uifiles folder, so you now have:
C:\Program Files\Sony\EverQuest\uifiles\Freq_di28889
First time I used this UI it happened to me also, where I could not load it.