This is causes of inconsistent.
Run the report RSSNR0T1 with number range object MATERIALNR from SE38. Refer to this OSS note 11294 - Not possible to add number range groups
System will remove all groups which has inconsistent.
(Note: System will remove all other groups which has inconsistent with number range, so you need to be careful before run this report. First run the program in your development system and check the result.)
**Edited by: Dibyendu Patra
