"VDC Group with existing firewall groups cannot be deleted"VMware Cloud Director 10.6.X
The issue occurs when there are IP Sets, Static Groups or Dynamic groups still associated with the Firewall Rules for the edges that are included in the DCG.
To workaround the issue please check if there are any IP sets on the Datacenter group which can be deleted and try to delete the Datacenter once the IP sets have been removed.
To delete the IP set(s) please follow the below steps:
Networking > Data Center Groups.Security > Static Group > DELETE button to delete any Static group(s).IP-Sets and Dynamic Groups.