If you have mIRC set to choose a random port from a range of ports, try changing this to just one port, for testing purposes. It may be that some of your ports are forwarding but others are not. Range mismatch? Try selecting big numbers for port values, between 10000 and 64999, so there is less likely a conflict between mIRC and other software.
I ran a scan on my ports and found one in the eight thousands that's open. I set mirc to use this port by setting it as the first and last port. I ran the server overnight to test it and it succeeded 4 out of 34 times.
Any idea why setting it to an open port made no difference?
