Error: A general system error occurred: Error Stack Call “IscsiManager.QueryCandidateNics” for object “iscsiManager” on ESXi “<Your Host Here>” failed
You may run into this error on VMWare ESXi hosts when trying to modify the network interfaces used for iSCSI.
I normally see it happen when someone messed up or entirely removed the NICs that were in use for iSCSI without first removing them from the iSCSI bindings.
The only way I’ve found to get rid of this error is to connect to the host using the application client (web client gives a “general error” and doesn’t allow you to do anything). You can still connect directly to a host in vSphere 6.5 using the 6.0 client. You will need to first disable and remove the iSCSI software adapter, and then remove the iSCSI configuration files and reboot.
Needless to say, shut down or migrate all VMs and make sure there is no disk I/O activity towards iSCSI on the host.