All the Volume Groups visible to a system need to have different names. Otherwise many LVM2 commands will refuse to run or give warning messages.

This situation could arise when disks are moved between machines. If a disk is connected and it contains a Volume Group with the same name as the Volume Group containing your root filesystem the machine might not even boot correctly. However, the two Volume Groups should have different UUIDs (unless the disk was cloned) so you can rename one of the conflicting Volume Groups with vgrename.