Some time the ~{!0~}Run Now~{!1~} button is disable and some time it is enable. How to control the ~{!0~}run now~{!1~} button enable or disable status?

It is enabled when a job is selected and it can be run.
It is disabled when no job is selected or a selected job cannot be run (for instance if you run 24x7 as a service and open GUI in a separate instance).

: Some time the ~{!0~}Run Now~{!1~} button is disable and some time it is
: enable. How to control the ~{!0~}run now~{!1~} button enable or disable
: status?