unrecoverable error while applying the custom patch


I am dong the upgrade from SM9.20 to SM9.41 

My path of upgrade is SMv9.20 -- SMv9.31

SMv9.31 -- SMV9.31PD

SMv9.31 PD -- SMv9.41 P4

We did the upgrade in development environemnt and created the custom patch. 

I did the upgrade in QA environment and it was successful. Now before the production move, i am trying to repeat the upgrade in one of a sandbox environment.. 

I am able to upgrade the application till SM v9.31 PDCP3.

While trying to upgrade from SMv9.31 PD3 to SMv9.41 P4, i am getting the error while applying the custom patch .

The record being added contains a NULL key (message,add.schedule)
file:(schedule) key:(schedule.id=) (message,add.schedule)
Key #7 is empty. (message,add.schedule)
Invalid connection type (apm.upgrade.import,connect.qsam)
unable to open connection (apm.upgrade.import,connect.file)
unable to open connection (apm.upgrade.import,connect.default)
Unrecoverable error in application:  sm.upgrade.ux on panel call.apply.upgrade
Unrecoverable error in application:  apm.upgrade.wizard.ux on panel load.upgrade.inf
Unrecoverable error in application:  apm.upgrade.load.objects on panel load.upgrade.inf