Understanding Java Stack trace error log -could not send push notification

Happy New Year Folks,

Looking for some guidance understanding a java  stack trace log.

I am running SMC 3.6.

The first part of  error message says:

Message:

could not send push notification

Stacktrace:

com.smartphone_solutions.smartman.data.bo.exception.ApplePushNotificationServiceException: Could not send app apns push notification

                at com.smartphone_solutions.smartman.communication.applepns.APNSConnectionManagerForApp.sendAppPushNotification(APNSConnectionManagerForApp.java:345)

I have attached the full log to this post

My Questions are

What would cause this ?

Is it affecting only 1 or 2 devices or all ?

How do i fix it, if it can be fixed ?

Thanks in Advance

Jason