Resolution:
When starting applications from the Admin GUI, the tra hawk agent uses starts a new process to run the related application. And the the stderr and stdout of newly started process are redirected to tsm.log as StreamGobbler(ERROR) and StreamGobbler(OUTPUT) respectively.
The appearance of StreamGobbler(ERROR) in tsm.log file may indicate errors happened during the application starting up or any other error that would appear in the two streams mentioned above.