I may have a similar issue. I just got a Buffalo ZR-HP-G300NH and flashed the latest DD-WRT firmware (don't have specific version number).

Here is the interesting part. When I use no encryption, I am unable to see/connect to the AP. However when I use any encryption to (WEP, WPA2, etc) I am able to see and connect to it.

I am using the same sid as my old linksys WRT54G (also running DD-WRT). Do you think it could have something cached that associates the MAC and sid of that particular AP?

Any ideas how to resolve? FYI, I want to keep my AP open (no encryption).