Calling ME22 BDC after PO BAPI - error PO is already processing by user xx

Hi,

I am calling BAPI for PO change and after changing I am calling BAPI commit, after that I am call BDC for ADD some data to PO but it is giving error that PO is already processed by user.

Could any one tell me what to do before calling BDC in the same program.

thanks

bobby