Error Message :
U00015000 WP 'UC4T#WP001' cannot be primary, because it is using another MQSet than the old primary WP ('2' instead of '1'). Please start a WP with an older version.
Occurs when an upgrade is attempted without "Zero downtime upgrade" and where 'UC_SYSTEM_SETTINGS' parameter ZERO_DOWNTIME_UPGRADE = Y.
Release: 21.0 and earlier
Set the value ZERO_DOWNTIME_UPGRADE = N in the 'UC_SYSTEM_SETTINGS'
Restart upgrade procedure