Have you read this excerpt from http://support.apple.com/kb/HT4199
WPA2 Personal (AES) is currently the strongest form of security offered by Wi-Fi products, and is recommended for all uses. When enabling WPA2, be sure to select a strong password, one that cannot be guessed by third parties.
If you have older Wi-Fi devices on your network that don't support WPA2 Personal (AES), a good second choice is WPA/WPA2 Mode (often referred to as WPA Mixed Mode). This mode will allow newer devices to use the stronger WPA2 AES encryption, while still allowing older devices to connect with older WPA TKIP-level encryption. If your Wi-Fi router doesn't support WPA/WPA2 Mode, WPA Personal (TKIP) mode is the next best choice.
Note that the use of WEP is not recommended for compatibility, reliability, performance, and security reasons; WEP is insecure and functionally obsolete. However, if you must support legacy WEP devices and you have a newer (802.11n) Wi-Fi router, you may be able to select the WEP Transitional Security Network (WEP TSN) security mode. This mode will allow legacy WEP clients to join your network with WEP encryption while allowing newer devices to use more modern and secure encryption modes, such as WPA TKIP or WPA2 AES. If WEP TSN mode is not supported, then WEP128 with Shared Authentication should be used (with a single WEP key in key index 1). For compatibility reasons, WEP128 networks should use 13-character ASCII passwords.
Make absolutely certain that the Blu-Ray player is using the same protocol as your Express.