[kall]

I'm afraid I am far too unwell to explain the entire vBulletin Hook system at the moment.

Basically, it was introduced with vB 3.5.x (the version that recently came out, replacing 3.0.x), allowing coders to make 'hacks' that did not require code modifications.

Effectively, the php file is run, then when it comes to a 'hook' in the code, it looks in the database to see if anything additional is in that hook.

By doing what you suggest, the php file will not look for that hook if the post is being Previewed. You need to go to the hook in your Plugin Manager and add the conditional you added to the php file in the hook for Ucash.