I am doing some validations in the userexit_move_field_to_vbap and showing an error message after that. Also I am using BAPI_MATERIAL_AVAILABILITY FM in the user exit. While changing or creating the sales order, when the my error pops up, after pressing the enter button for 3 or more times, I am getting the error ' Incorrect index structure for table XMVERF_POS/line item number '. Can you please help me out here. How to avoid this?