It's probably a Yahoo problem with their new Neo format. They have screwed up a lot of groups. The group is most likely still there, but you may have to wait until some of the problems get fixed. Here are links to some info about Neo:
http://forums.whirlpool.net.au/archive/2148098
http://www.thereminworld.com/forums/t/29072
I should add that there seem to be different problems associated with computer access, iPad access, smartphone access, browser type, etc. You might want to try accessing through a different media.