I use a notebook with an optional PCMCIA wireless card. When the card is not plugged in, device wlan0 doesn't exist, but the plugin still sits in the panel. Because the panel graphics are too big (compare with other mem/cpu/net panel plugins), it takes up too much space. It should either auto-hide even when the device is not present (ie. card is not plugged in, therefore signal can't be measured anyway) or the lugin should be redesigned to save space like other plugins (eg. http://xfce-goodies.berlios.de/images/xfce4-battery.png )
I have fixed this in 0.5.2 release, shortly to be released to http://jameswestby.net/debian/ I have added the option to hide when the device is not found, with a warning that this will make it hard to remove or configure the plugin when there is no device. (I will close the bug if I am granted and account with sufficient permissions)
Good, now it works just fine. Thanks a lot.