An often made mistake when trying to open up or close a port range with the ESX(3.0.2 and 3.5) firewall is using the dash(-) as a divider. Using the dash unfortunately does not always result in an error. To open up or close a port range you should use a collon(:) as a divider:
esxcfg-firewall –openport 6000:6010,tcp,in,test