"An exception of class NilObjectException was not handled. The application must shut down."

There are many threads about this...

https://jamfnation.jamfsoftware.com/discussion.html?id=4426

I think most of the time it's diskless booting

http://www.macos.utah.edu/documentation/administration/setup_netboot_service_on_mac_os_x_10.6.x_client.x_client/setup_netboot_service_on_mac_os_x_10.6.x_client-diskless_netboot.html

Is the machine still checking into the JSS? The only time I've seen this happen from my experience is when the machine can't talk to the JSS, or the JAMF binary is missing or unavailable (hung perhaps?). Try running jamf checkJSSConnection to check the machine's connection to the JSS. If it isn't, try re-enrolling.

What OS version are you running on the device that you are trying to launch Casper Admin on?

I saw this error when running OS X 10.11 beta and Casper 9.8...

Updating to 9.81 fixed the issue for me since its supports 10.11

@spotter I think that's what it is. I'm on 10.11 now. Thanks for the replies guys.

happy to help...

Thanks to you all, I was just trying to add a new printer and kept getting this message. I was planning on upgrading to 9.81 next week, looks like I may have to do that sooner. Love this community!