A customer placed order to switch their VPS subscription to another Service Plan. Order provisioning fails in PBA with the following error message displayed on the 'Service Status History' tab in the subscription properties:
Change Service Plan failed: Parallels Operations Automation error #extype_id #79, module_id #VEManager, Cannot upgrade to a new VPS config - different OS templates (RT OS template ID 921, VPS OS template ID 1139).
Provider incorrectly configured the list of allowed upgrades/downgrades for the Service Plan the problem subscription is based on - PBA allows to upgrade VPS subscription to the POA Service Template which includes incompatible target VPS resource.
E.g. Provider allowed PBA to upgrade Service Plan based on Service Template with CentOS 5 VPS resource to Service Plan based on Service Template with CentOS 6, Debian, RedHat or Ubuntu VPS resource. Another possible case is that PBA allows to upgrade Service Plan with x86 VPS to Service Plan with x86_64 VPS or vice versa. Such upgrade will fail in POA.
POA allows to upgrade VPS only within the same OS template family and architecture, e.g. subscription with CentOS 5 x86_64 VPS may be upgraded to a Service Template with CentOS 5 x86_64 VPS Resource Type.
The failed upgrade order should be canceled in PBA, it is not going to be completed.
Then, Provider has to carefully analyze list of allowed upgrade/downgrade options for their Service Plans in PBA to exclude possibility for a customer to place wrong order on Service Plan switch. The rule to allow switching between plans is simple - VPS Service Plans should allow to upgrade/downgrade subscription only within the same OS template family. PBA must not allow to place order to upgrade VPS to incompatible OS template.
After the list of allowed upgrade/downgrade Service Plans is corrected for the Plan the problem subscription is based on the customer may place order on Service Plan switch once again.