Jmeter: got java.io.IOException: Unable to tunnel through proxy

Question

Hi there,

like I wrote in the subject, I got this error while using Jmeter, I ran a script thread which connects to a site and does a series of http operations, my Jmeter launch script is configured this way:

PROXY="-H <IP> -P 80 -u <user> -a <password>"

Actually I just masked the real informations, but IP, user and password are set and correct.

java $SERVER $JVM_ARGS -jar `dirname $0`/ApacheJMeter.jar "$@" $PROXY

Jmeter starts correctly, but when I run my thread script this is the answer I found in my Result Tree as Http Response to the first call:

java.io.IOException: Unable to tunnel through proxy Proxy returns "HTTP/1.1 403 Forbidden"
at sun.net.www.protocol.http.HttpURLConnection.doTunneling(HttpURLConnection.java:1472)
    at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:164)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.connect(HttpsURLConnectionImpl.java:133)
    at org.apache.jmeter.protocol.http.sampler.HTTPSampler.sample(HTTPSampler.java:457)
    at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:889)
    at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:875)
    at org.apache.jmeter.threads.JMeterThread.run(JMeterThread.java:298)
    at java.lang.Thread.run(Thread.java:619)

I checked all the parameters and I am sure they are correct, is there everything else I need to check before asking sysadmins?

Thankyou