Hi Kunal,
This really a good observation. We also have seen this type of issue in the past, but the order was not in SNP production horizon/extn. prod. horizon. So, after we found the the order (where there was no valid PPM/PDS), we deleted the order to resolve the issue. Basically those orders are hanging orders with no capacity consumption in resourse.
Now, I guess when capacity leveling program starts it select all the orders available in the leveling horizon and do the consistency check. After this task is finished its start to perform the leveling job and this time its exclude the orders which falls in the horizon (based on the setting in the profile).
So, in your case the job is failed in the first step itself.
Thanks,
Satyajit