http-get doesn't work when server (load balancer) is up


I'm running ServiceMon Version, i'm sending http-get requests and monitoring their responses.

When the web server is out line or down ServiceMon works fine, because the response is something like "Error occured at ... Unable to connect to the remote server". But when the server comes back, the app continues to send the same (like t) error instead of the correct response. The server is up but the monitor response is like down.
This only occur in a web server with load balancer.

Please, How to solve this issue?