Hi Rajesh,
I have faced a similar situation in the past even though commitment item is maintained in GL master and you use the function module to derive it the system does not derive the commitment item.
In my case it turned out to be an authorization issue.
So do the following:
Create a new derivation rule and for the GL account assign the commitment item in the derivation rule. Then check if the system is deriving the commitment item. If this works, then deactivate the derivation rule and run the scenario again and when the error comes up check for missing authorization using /nSU53.
Keep me posted if this solves your issue.
Regards,
Insomniac