D-Link AirPro DWL-AB650 Installation Manual page 14

If the Access Point is configured to use WEP, you must enter the
appropriate WEP keys in the WEP key fields above. These WEP keys
must be exactly the same as the WEP keys in use by the Access Point. If
they are not exactly the same, your Cardbus Adapter will not be able to
access the wired network through the selected AP.
There are three distinct modes of operation for the connection between an
AP and your DWL-AB650 Cardbus Adapter, in terms of WEP encryption.
The first is unencrypted. That is, WEP is disabled on both the AP and
your Cardbus Adapter. The second is the Network Authentication
(Shared Mode). When this box is checked, the AP and your Cardbus
Adapter will only verify that the exact same WEP keys are in use by
sending each other encrypted messages. After this authentication, all data
transfer between the AP and your Cardbus Adapter will be unencrypted.
The third is Enable Data encryption. In this mode, all data exchanged
between the AP and your Cardbus Adapter is encrypted.
All encryption settings, the four WEP keys, the Network Authentication
(Shared Mode), and the Enable Data encryption settings must be exactly
the same on the selected AP as they are on your Cardbus Adapter for data
transfer to occur. If you are unsure of the encryption settings in use on
the AP, contact your network administrator.