Edge gateway <name> has Org VDC networks attached to it. Please delete the networks before attempting to delete the edge gatewayOn the Tenant or Provider portal, Enable and then Disable Distributed routing on the Edge which the error complains about.
Once the tasks complete re-attempt the deletion of the Organization VDC or Edge in question.
If the issue still persists, contact Broadcom Support and note this Article ID (325525) in the problem description. For more information, see Creating and managing Broadcom support cases.