Can't delete info in backup GlobalCatalog file

Microsoft Windows Vista Ultimate 64-bit Service Pack 1

My backup drive D: is too full to accept another nightly backup of drive C:.
I can manually delete the many older backup sets I no longer need but the
reference to them in the GlobalCatalog remains. Under drive D: "Properties"
I've tried using "Disk Cleanup" removing the "System Restore and Shadow
Copies" but no backup sets or reference to them in the GlobalCatalog are
removed.

Is there any way I can delete the reference to deleted backup sets that
remain in the GlobalCatalog for these backups?

Thanks very much for your time in reading and offering any suggestions or
solutions you may have.
Rick