tmtools/utils/common.sh uses tmtools/share/debuggee/PortScanner.java to find unused ports and assigns it's output to variable PORT. After JDK-7162400 output may contain warning message about stale pid file.
In this case value assigned to PORT will be look like:
"Java HotSpot(TM) Server VM warning: failed to remove stale attach pid file at /tmp/.java_pid19056 10000"
This value will be passed to DebuggeeStarter and it will fail with:
Exception in thread "main" java.lang.NumberFormatException: For input string: "Java"

See example:
http://aurora-ds.us.oracle.com:9500/runs%2F271722.JAVASE.NIGHTLY.VM.Main_Baseline_hsx24.2013-08-14-266/results/ResultDir/complex_scenario/myclient/client.log
http://aurora-ds.us.oracle.com:9500/runs/271722.JAVASE.NIGHTLY.VM.Main_Baseline_hsx24.2013-08-14-266/results/ResultDir/complex_scenario/ComplexScenarioDebuggee.err