This Error indicates an attempt to flash a project to the board while a Debug Session is still running. Only one project can be debugged or run at the same time.
From the debug perspective, make sure all sessions are terminated before deploying a new project. i.e:
Toolbar Menu > Window > Open Perspective > Debug
1. Select the running projects you want to terminate.
2. Right click and select the "Terminate" button
It is important to verify that there are no open debug sessions running before Running/Debugging a new project