From the exception that you have provided it seems that you might have deleted the application that you wanted to gain insights from. We need some more details so as to troubleshoot the problem. This would also require agent logs. I request you to contact us at support @ site24x7.com with your agent logs to trouble them further. I'm sure we'll be able to figure it out.
If you have any questions on the usability or the metrics that you would like us to give you for a better experience feel free to post here.
Product Manager, Site24x7.