dmesg:
wlan_wep: disagrees about version of symbol ieee80211_crypto_unregister
wlan_wep: Unknown symbol ieee80211_crypto_unregister
wlan_wep: disagrees about version of symbol ieee80211_crypto_register
wlan_wep: Unknown symbol ieee80211_crypto_register

/var/log/messages:

Mar  5 20:34:47 mythbox modprobe: FATAL: Error inserting wlan_wep (/lib/modules/2.6.12-1.1381_FC3/updates/net/wlan_wep.ko): Unknown symbol in module, or unknown parameter (see dmesg)
Mar  5 20:34:47 mythbox kernel: wlan_wep: disagrees about version of symbol ieee80211_crypto_unregister
Mar  5 20:34:47 mythbox kernel: wlan_wep: Unknown symbol ieee80211_crypto_unregister
Mar  5 20:34:47 mythbox kernel: wlan_wep: disagrees about version of symbol ieee80211_crypto_register
Mar  5 20:34:47 mythbox kernel: wlan_wep: Unknown symbol ieee80211_crypto_register
Mar  5 20:34:47 mythbox ifup: Error for wireless request "Set Encode" (8B2A) :
Mar  5 20:34:47 mythbox ifup:     SET failed on device ath0 ; Invalid argument.