Billing document does not Exist-number skipping?

Hi friends,

i am facing a issue related to billing documents does not exist-in VF02-error  Message no. VF041!

i checked forum and as per suggestions ,checked for archiving docs but found nothing.

Even at table level VBRK billing number does not exist.No buffering maintained for Number ranges.(internal)

some number ranges e.g. from 77-83 are not existing..What could be possible reasons.?

As billing numbers 76 exist and 84 on wards also exist in system.Also number range is of same Billing type.

kindly guide for suggestions to find exact cause to be given to client!!

regards,

V.c