I'm getting these problems with Netscape but am managing to overcome them.
Netscape starts to load Mudcat but then the 404 message comes up.
If I then use my back button Netscape usually continues to load normally (although on occassions I have had to use the back button two or three times).
I then read the threads by using the right click - open in new window - which works normally and means that Netscape isn't having to refresh all the time.
It's a little inconvenient but it works OK.