Proxy Error 502

Hi,

I am getting the following error. The Apache server is a proxy webserver 
connecting to a virtual ipaddress ( clustered cms server). Could you please 
tell what is the resolution ?

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Proxy Error
The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST /iw/webdesk/login.

Reason: Could not connect to remote machine: Connection refused

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