Symptoms:

In the Wireless Settings screen of your NETGEAR wireless router or access point, the WEP security option is missing from the list of security options.

Cause :

The wireless settings are set to give a high speed connection.
WEP is only supported in the old 802.11b (11Mbps) and 802.11g (54Mbps) wireless standards. Later standards support higher wireless speeds, but do not support WEP security. WPA or WPA2 security must be used. Only WPA2 will give full wireless speed.

Solution:

Ideally, just use WPA2 instead of WEP.
If you really must use WEP, change the Mode setting on the Wireless Settings screen to "54 Mbps (802.11b/g)".
Be aware that this will make all your wireless connections much slower than the router or access point is capable of.