getting error " 502 proxy error. The requested resource is in use. (170)." on the upstream proxy TMG servers

This one is about a case, where Admin had configured Two TMG 2010 upstream proxy servers and he had two TMG 2010 downstream proxy servers. Users started reporting that they intermittently get error ” 502 proxy error. The requested resource is in use. (170).” while accessing internet. At the time of issue, even if you try…