1) Cisco Unity Express was shipped from Cisco with version 7.0.1 or later
2) One of the following upgrades is done
– 7.0.x to 7.1.
– 7.0.x to 8.0.
– 7.1.x to 8.0.x
Given that this was CUE 8.5.1 running on an SRE, it doesn't match the criteria. Fortunately the workaround does still work - use the CUE CLI command software uninstall uid-list 26bd663c-3e5a-43d9-a6c3-5441ce44941b & once it has finished rebooting you can proceed the with the upgrade.