Create New Site Link BROKEN, how should I fix it?

I asked this question on another request but Im not getting support.

On my multisite setup, the "Create New Site" Under My Sites tab on the admin is broken, its pointing users /wp-signup.php when it should pe pointing them to /pro-site/?action=new_blog and I know the plugin should do set it automatically but for some reason is not. I need a fix that won't break with plugin (or wordpress) updates. your help will be greatly appreciated!