Once my machine is VLAN enabled, I\'m neither able to prepare new scripts using JMeter-2.9 tool nor able to execute my old scripts which I used to run earlier on the same machin
According to me issue is related to proxy.
Jmeter sits between your machine and proxy and thats how it records all the requests coming to and going from your machine. It doesnt matter you are in VLAN or WAN if your proxy settings are correct.
Please check your proxy settings once put apply similar proxy settings (Localhost,8080)
in VLAN or else you can provide seperate proxy for your Jmeter by starting it with JMeter parameters,
Jmeter.bat -H <hostname> -P <port> -u <username> -a <pwd>