Regarding Confirmation Key change in PO

Hi Experts!

I have a problem. I am using BAPI_PO_CHANGE to change the confirmation_key

in poitem table. It is working fine if there is no partial gr against that line item.

But if there is a gr entry against that line item its giving me a message 'confirmation key should not be changed'..

Is there any way you guyz can help me out with that.

thanks