CABMeeting script include is in scoped app so you have to give fully qualified name domain + script include name.

sn_change_cab.CABMeeting(gr)

Also, here is the sample code I just ran for quick testing in the background script and its working fine. 

var gr = new GlideRecord('cab_meeting');
gr.addQuery('sys_id', <sys_id>); // replace sys_id with any Cab meeting sys id.
gr.query();
gr.next();
gs.print(gr.getRowCount());

var notifiedAttendeesCount = new sn_change_cab.CABMeeting(gr).createCABAttendeeNotifyEvents();
var infoMessage = notifiedAttendeesCount > 0 ? gs.getMessage("Notifications sent to all attendees") : gs.getMessage("No notifications sent as there are no attendees");
gs.print(infoMessage);

Replace <sys_id> with one of your Cab meeting sys ID in the above code and test in background script and see the output for reference. after that you can modify this as per your need

Let me know if you face any issues.

Please mark this accepted & helpful, if it helps.

Thanks & Regards,

Sharjeel

Hi Sharjeel,

It is working by hardcoded sysid.Now I need to fetch meeting sys_id weekly- may be in encoded query, which is not happening

It is wrking now after removing @

Glad It works! Happy Coding.

Kindly mark the appropriate response accepted and helpful so that others can be benefited by this and this thread can be closed as solved.

Thanks & Regards,

Sharjeel