Dear Krishna,
Mentioned error is coming due to number range buffering issue,
Request you to go to your number range Maintainance for Billing i.e.SNRO enter your billing object as--RV_BELEG, check the setting of Buffering in Edit---Buffering, if it is blank then maintain the number in between 15-20 & if the Number is maintained in Buffering then make it in the mentioned range.
Hope this will resolve your issue..
Share your feedback.
Regards,
Amit Jewalikar.