When performing upgrade of subscription from Exchange 2010 to Exchange 2013 following the guide, following error is displayed in POA:
Could not upgrade organization '<OU>' to next Exchange version. Migration of subscription <SUB_ID> from Exchange Server version 2010 to 2013 is not possible.
or in PBA:
Change Service Plan failed: Parallels Operations Automation error #extype_id #115, module_id #Exchange, Migration of subscription <SUB_ID> from Exchange Server version 2010 to 2013 is not possible.. .
Migration of subscriptions from Exchange 2010 to 2013 is available in POA starting from update POA 5.5.3, please see the release notes
Upgrade POA to version 5.5.3 or higher.