Can you verify that no debug session has been already launched. Go to the Debug perspectie (Windows > Open Perspective > Debug (or Other... > Debug)) then terminate every opened sessions.
Can you also check in the task manager if an openocd.exe is still runnning in background ? If it is, kill the openocd process.
Then relaunch the debug. If the same error is displayed, please copy the openocd process output (on the Debug perspective, select the openocd process under your debug session, the output should be displayed on the console view).