Product: S5500T version V1R5. FC link, HBA type - FC - two switches betwen host and storage.
The customer tried to remove a host from host group from ISM but he was not able to do that. he received the below message:
The custoemer tried to remove the initiators that belong to the involved host [ISM / HOSTS tab, right click on the host, chose Initiators and remove it/them] but also he received an similar message from ISM like above picture and he was not able to delete/detach the initiator from the host.
So, the problem was when he trid to remove the initiator from the host.
A solution for this kind of issue is to stop the I/O flow from the involved host to the storage ( to stop the application from the host if it's possible) and after that we have to try again to remove the FC_initiators ( in my case were FC-initiators and not an iscsi-initiator) . If the storage detect an I/O request will refuse to remove the initiators.
In my case the customer stoped the port from his switch and after that he was able to remove the initiators also the host from the host group.