I'm using the yaromat check form extension and when I add Pure PHP upload, it checks the form but if there's an error, I can see it but the pure PHP upload makes still the insert and even if I didn't choose a file to upload (and disable the "File required")... any idea what to do or what I'm doing wrong?
You need to put the upload javascript on top of behaviors list instead of the check form javascript. To do so:

Select the <form> tag

Go to the Behaviors pallete

Make sure that the Pure Upload javascript is on top of the behaviors

And that the Check Form behaviors is below - if not correct with the arrows

NOTE: This is valid if you use Yaromat Check Form or the standard Check Form behavior.