Proxy server received invalid response

Hi All,

I have Vaadin 6 application running on tomcat 7 on my local.

it was running successfully on testing environment till present.(tomcat8)

Now after some enhancements , it is again deployed on testing env(tomcat 8)
(running properly on local(tomcat7)).

but is throwing an error.I dont understand that error.Please see the attached screenshot

Communication Problem
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(Syntax error): unexpected identifier “Original JSON text:HTML PUBLIC " //IETF/DTD HTML 2.0//EN”?
Proxy Error
Proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST/ztime/UIDL. Reason: Error reading from remote server

Please if any one can help me, will be appreciated.