Why
Sometimes the Agent application will become minimized and is difficult to restore. When a user attempts to launch the app, it errors and will not run because it is already running. Resulting in the “Only one agent can be run at a time” error displayed on the screen…
Fix
Open Taskmanager by right-clicking on the system tray, and selecting "Task Manager"
Confirm you are viewing Processes, and sort by Apps.
Right-click on Agent (32 bit) and select End Task.
If there is more than one Agent, you will need to repeat the end task for all Agents listed.
Wait about 5 seconds.
Close Task Manager
Launch the Agent as you normally would.
If the error persists, please reboot and try again.