When attempting to activate a plugin, the following message is displayed:
"The Plugin Activation button is not available because the system is currently upgrading"
Cause #1. An upgrade is still running. To verify an upgrade is still running go to System Diagnostics --> Upgrade Monitor.
If it's still running, the following will be displayed:
Cause #2. Scheduler workers are not running on the node due to the instance being in 'debug mode'.
If no upgrade is running we will see the following:
Go to /stats.do to determine if the scheduler workers are running on the nodes. If they are running, you will see the following:
Resolution #1. Allow the upgrade to complete
Resolution #2. If no scheduler workers are active on the node, please open an incident with ServiceNow Customer Support.