AdRotate sets no limitations on scripts like that. And certainly not using 403 error pages.
A 403 error means you have no access to a page or file on your server. That’s usually done with .htaccess or from your hosting dashboard. .htaccess is, among other things, a access control feature in servers which can be used by security plugins such as Wordfence or Sucuri.
Perhaps they think the file you’re using is infected with malware (or it actually is).