Validation Callbacks!!!

[eluser]reset[/eluser]
Hello Bramme, I attach one file with two screenshot.

- The first is the initial state for the user.
- In the second, the user selects all options in the first "multiple select" and put into the second in the order that he wants.

I must validate that first multiple select is empty, and I have tried the options that I related in the first post.

Thanks