The IEEE 802.11b specification defines only 40-bit Wired Equivalent Privacy (WEP). Cisco and other vendors have independently extended the specification by implementing their own versions of 128-bit WEP, which may not be compatible with each other.
If WEP is required between devices from different manufacturers, configure all such devices to use 40-bit WEP.
Associated but cannot pass any traffic
Client / Device cannot authenticate
WLAN adapters (wireless card) / ACU (Aironet Client Utility)