Since it was working before Mountain Lion, with, presumably, similar file
sizes and numbers of items, I'm thinking the advantage of text item
delimiters is that now you can use a list of items as delimiters, which
could work better than doing the repeat loop and the "contains" test.

Unless there is some reason why a doing this on a list with thousands of
items would have worked before mountain lion but not work with mountain
lion.

Do we know of a mountain lion specific issue?

ES
 

>> set thePieces to splittext bigFile using "whatever"
> 
> Are you doing a literal split or a regex split with the splittext command? if
> the former, why not use text item delimiters instead? If the latter, there was
> a problem with it reported over on macscripter.net recently.
> 
> But perhaps the more important question is how many items thePieces contains.
> If it's many thousands, you're going to want to break the job into smaller
> parts.