Error using JMeter

Hello,

I would test my application with JMeter. I followed every instruction in
https://vaadin.com/it/wiki/-/wiki/Main/JMeter%20Testing
but i receive this error:

org.apache.http.client.ClientProtocolException
	at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:909)
	at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:805)
	at org.apache.jmeter.protocol.http.sampler.HTTPHC4Impl.sample(HTTPHC4Impl.java:284)
	at org.apache.jmeter.protocol.http.sampler.HTTPSamplerProxy.sample(HTTPSamplerProxy.java:62)
	at org.apache.jmeter.protocol.http.sampler.HTTPSamplerBase.sample(HTTPSamplerBase.java:1075)
	at org.apache.jmeter.protocol.http.proxy.Proxy.run(Proxy.java:212)
Caused by: org.apache.http.ProtocolException: The server failed to respond with a valid HTTP response
	at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:103)
	at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:62)
	at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:254)
	at org.apache.http.impl.AbstractHttpClientConnection.receiveResponseHeader(AbstractHttpClientConnection.java:289)
	at org.apache.http.impl.conn.DefaultClientConnection.receiveResponseHeader(DefaultClientConnection.java:252)
	at org.apache.http.impl.conn.ManagedClientConnectionImpl.receiveResponseHeader(ManagedClientConnectionImpl.java:191)
	at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:300)
	at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:127)
	at org.apache.http.impl.client.DefaultRequestDirector.tryExecute(DefaultRequestDirector.java:712)
	at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:517)
	at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:906)
	... 5 more

What is wrong?

I’m using Vaadin 6.7.9