There was a
similar post discussing the same issue recently, where UPnP was behaving intermittently. In my tests, described in the above post, I experienced the same intermittent behaviour when using both mIRC and a UPnP monitoring tool, which was designed to monitor UPnP activity. It would work fine most of the time and then suddenly, it would stop working. I eventually tracked it down to my firewall, which when disabled allowed mIRC and the UPnP tool to work all the time without any issues. Beyond that, I am afraid I have no explanation. It may just be that UPnP is unreliable.
