Application installation is unavailable because another operation is running: Plugin Activation for 'plugin name'

Admin users on domain separated instances with domain delegated administration enabled can see the following when trying to install a plugin although no plugin is currently being installed:

Seen in New York

When 'Domain delegated administration' is enabled the user must comply with the following constraints in order to activate plugins:

1. Have the 'Admin' role
2. Not be a read-only user
3. Must be in the 'global' domain

If the 'Domain delegated administration' property is set to true, make sure that the administrative user is in the 'global' domain.

PRB1363926 is currently being reviewed to correct the message