Hi Robert,
This error is seen if the device is a single node and node is set to primary. Thus, at the time of upgrade , ISE thinks there is secondary node (as this is primary node) and expect to upgrade the secondary node first.
Make sure this node is standalone.
Go to Administration > Deployment > General Settings > Role : Standalone.
Make sure the role is Standalone and then click on SAVE to confirm and try to upgrade ISE.
Note: Do take a backup before making any significant change on the devices.
Regards,
Dinesh Moudgil
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Cisco Network Security Channel - https://www.youtube.com/c/CiscoNetSec/