[WetWired]

Well, the userinfo variable applys to the current logged in user, not the user with the post. Also, WWU002 is a prefix to denote variables used by the plugin uniquely identified by 'WWU002' (activity modification); no reason to keep it for your own plugin.
You should probably be using $post['points'], as this seems to be the variable for the posting user's points. Also, if uCash allows a negative ballance or if $post['points'] has a decimal point, the code will need to be modified.

For figuring out what's going on in your code, I suggest enabling debug mode, and using calls to devdebug() with the variable you want to see the value of, which will put it in a dropdown box that will appear at the bottom of the page.