Error Message :
U00011898 Switch server mode to DWP not allowed during Zero Downtime Upgrade.

The following two hints were missing in the overview section of the Zero Downtime Upgrade (ZDU) documentation: 

• While you are in compatibility mode, you are not allowed to switch a Worker Process (WP) to a Dialog Process (DWP). 

• When an Automation Engine process running the old version stops, it cannot be restarted. When all Automation Engine processes running the old version have stopped (e.g. because of a power failure), the ZDU finalizes the upgrade process. No rollback is possible in this case.

Cause type:
Other
Root Cause: N/A

OS Version: N/A

Update to a fix version listed below or a newer version if available. where the above two hints are now included in the overview section of the ZDU documentation.

Reference

Automic Workload Automation 12.1 Documentation:
Installation Guide > Upgrade Installation > Zero Downtime Upgrade > Upgrade Process

Fix Status: Released

Fix Version(s):
Component(s): Automic online documentation

Automic Online Documentation 12.1.0 - Available

Workaround :
Do not switch to mode DWP or stop the server processes running the old Automation Engine version while performing the ZDU.