Directly after update of the commandserver to version 5.3 on Windows, the GUI login might fail.
The service NBK OpenEJB server needs an additional start cycle to apply configuration changes occasionally.
Login to the commandserver on OS level.
Open the service menu (start->services.msc).
Stop the service NBK DC OpenEJB server.
Restart the service NBK DC Derby DB.
Start the service NBK DC OpenEJB server.
Start the GUI and log in.