I can confirm this issue with jss 8.6.0 and that ... setup_netboot_service_on_mac_os_x_10.6.x_client-diskless_netboot.html
DOES NOT FIX the issue.
I have made 3 different netboot sets for 10.8 and tried them with and without Utah netboot.rc mods. Last time I saw this issue had to apply a combo updater over top of a clean install then create the netboot set. Bad news is there is no combo updater at this writing for 10.8. Anyone have any luck netbooting OS X 10.8.0. For the record same iMac (4 gig ram) and other test mac mini(4 gig ram) machines netboot to 10.6.8 and 10.7.4 .nbi's and run casper imaging with no problems.
We have been getting "An exception of class NilObjectException was not handled. The application must be shut down." error in Casper Imaging 8.61 and still now we are running 8.64 and we are still getting the error. @Ajezard could be right that this occurs in Mountain Lion.
Our JSS server is running on OS X 10.8.3 and our images are also OS X 10.8.3. Our netboot server once live in OS X 10.8.2 now 10.8.3 but since the NilObjectException error is constantly appearing, JAMF techs have suggested using NetSUS appliance to resolve this error. However I tell you that even the NetSUS appliance as a solution to netboot triggers the NilObjectException error.
AFP permissions are correct, diskless booting was checked for the NBI creation, I also have edited the rc.netboot file as suggested by @brj. Update after update of the JSS yet this issue isn't resolved. Last week we did not get the NilObjectException during imaging. Our first imaging this week triggered the NilObjectException. We were running JSS 8.63 then. Updated the JSS this week in hopes to have a fix then moved from using OSX for netboot to the netsus appliance. But still NilObjectException error still there. This morning we imaged a machine netbooting to the NetSUS appliance running casper imaging 8.64. The imaging process completed without errors. Except the imaged machine was missing the printers that were compiled with the selected image configuration. So I re-imaged again but can't, cause now the NilObjectException error is back. The NilObjectException error shows up before Casper Imaging window comes up. This is before a configuration is even selected. It would be nice to know what is being done while the Casper Imaging splash screen is displayed prior to loading the compiled configurations. This way we can isolate and debug the cause of the error.
I do want to know what triggers this error and why is it intermittent?
Just to resurrect an old post, I too have started getting that error!
My set up is:
Mac Mini Server running Mac OS X v 10.9.1
Brand new iMac (shipped with 10.9 - can't run 10.8.5)
Netboot image running 10.9
Trying to install a Base image of 10.9.1
JSS is running 8.71
Casper Imaging running 8.73 (yeah, I know)
And the only thing that stopped me getting the error was unchecking Erase Macintosh HD! I have a couple of Labs of these new iMacs to image and I need to be able to erase the HD as part of the process.
Any ideas - I will endeavour to upgrade the JSS to 8.73 in the meantime.