We are actually in progress of agent roll out - our concept is to handle 2 agents inside one Agent Group inside of System Profile. Due to misconfiguration we had created one Agent Group obsoletly. Now we try to delete this group in order to assign agents to other System Profile.
Unfortunately deletion fails it says "This agent group cannot be deleted because there are still agents connected to it. Please disconnect the agent "<OurAgentIdentifier>" first!"
We get crazy as inside of Agent Mapping overview of that agen group NO mapping is specified.
Even if there is no mapping specified there may still be previously connected agents connected to that group. They will still be connected if the mapping was there when they started up even if that mapping is removed and you'll need to disconnect these prior to removing it. If this is the case it should be as simple as restarting the collector that these agents are connected to which will cause them to look at the mapping again to decide which group to connect to and if there is no mapping they won't match.