I had an interesting thing with the YJ and a Huawei E5830 wifi modem. (It's the portable 3G Wifi Dongle)
When running in 802.11b/802.11g mode the YJ wouldnt connect and the sketch just hangs on WiServer.init(NULL) and I'm using WiServer.h
If I switch to just 802.11b mode however it worked fine, thought it might help as it was driving me mad as I was trying to set up a different wifi network to avoid the reset problem with Macafee UDP packets (viewtopic.php?f=13&t=275)