APS-20405 Instance of application with id 0 does not exist' error at APS 1.2 application TAB when "Embed application user interface" is enabled and application instance is not created yet
Hotfix can be downloaded here.
Use pa_updates_installer (https://kb.cloudblue.com/en/111323) to install this hotfix. Also this hotfix will be installed automatically during upgrade to POA 6.0.1 via pa_updates_installer. To install hotfix manually obtain its distributive from the link above and follow instructions found in file UPDATE.txt of distributive.