I know this is a very common issue, but every answer that I found said the same thing: make sure that your WebUIValidation.js is in the correct path.
I know that it is there, and I know that Page_ClientValidate() is returning false, because I put in some alerts. However, the page is still posting back and I can't figure out why..
If you want to take a look at the source, check here:
Just click search without entering keywords.