Another user or another operation modified data; to continue, open the window again

Hi experts,

I am creating Purchase order based on sales order using DI API. While updating i am deleting the purchase order lines and updating the Purchase order. After updating i am getting one error.

"Another user or another operation modified data; to continue, open the window again '' (RDR1) (ODBC -2039) [Message 131-183]"

Any idea!!!!