Version management

Dear All,

I have made a Service P.O and entered a Service sheet. After wards i have cancelled the item in the P.O by locking the same. Now i need to cancel the service sheet. When I am going to ME22N then after unblocking the item and saving the document following error message pops-up

No new version created because a message has not yet been transmitted

Can you help in sorting the problem

Thanks in advance