I'm using The Dude to find out which addresses I've used in my network (192.168.9.0/24).
I use "Discover" and The Dude finds about 80% of the addresses I have in my network, but some of them stay undiscovered. If I ping them (the undiscovered ones), they answer!
So I'm not sure what's wrong...

Some of them have more than one IP, but those second addresses belong to a different subnet, so that shouldn't mind.

Every IP is static, I typed it someday long ago, but I can't find my notes... and it's becoming more difficult to find unused IPs.
Among the equipment within the subnet we can find modems, ether and wlan in Routerboards, Linksys WRT54G and a few Windows PCs.

Any ideas?

Did you also try discovering with the 'reliable (scan each service)' instead of the default 'fast (scan by ping)' mode?

Yes, I did try, but nothing changed.
What else do you think I should try?

Am I too fool, or there might be something wrong with my network, or with The Dude?

Hm, no. If these undiscovered devices do respond to pings, than I wouldn't know why they're not discovered. Sorry.