Here are some ways to troubleshoot a problem flood. If you are still stuck or need assistance please contact support.
Check STDOUT and STDERR logs on your grid for any errors.
Your grid logs might reveal the source of the error, particularly any script compilation issues.
Write to a custom log
You can use a custom JMeter listener such as
Save Responses to a File to write to
/data/flood/results/ which can then be accessed from your archives.