Error while generating product receipt

Hi All,

I have created a new purchase order and when i try to generate a "Product Receipt" with voucher no 100000871 for that PO,the posting process is cancelled with the following error.

Error - "Voucher 100000871 is already used as of date 4/10/2014"

But when i checked in the table there is no record  with voucher no 100000871. 

Can i please know at what case i will be getting an error saying the voucher no is already in use.

Regards,

Rajee