Yes, it is a 10053 error.
Overnet is a file sharing program that uses TCP port 4662 and UDP port 11104. I am running WinXP, and I checked through the list of the first thread you mentioned and most of those don't apply to my system.
I will try different server ports, however as I stated before another IRC program, trilian, runs without these disconnections happening.
I would love to use and purchase mIRC if these errors could be stopped.