I really don't know. Did you just get an error message stating that the procedure failed, no further details?
Yes I suppose one reason for failure would be an excessively large reference corpus but that would be rather unlikely. I recommend you open each word list and eyeball it to see whether it looks plausible, doesn't contain weird words etc.
A simple reason for failure is that WS thinks the two wordlists are from different languages but the error message should say that.
Cheers -- Mike