The client requires 802.11b components that only exist in fairly new drivers. Often times the drivers that came in the box with your Wi-Fi card are several months old.
A typical symptom indicative of a non-compatible drivers is being unable to see signals in the client, when there are signals in the area.
The Boingo client checks for compatible drivers when it starts, and offers to upgrade your drivers when it doesn't find them. In most cases, the automatic driver update will update your drivers, but for some configurations, you will need to update your drivers manually.