Wireless Security

I'm having a lot of trouble configuring wireless
security. I have 3 computers that I'm trying to put on a
wireless network. Computer A is hooked up to the wireless
base station, and Computers B and C are using wireless
adapters.

The problem is this: I can get either Computer A and
Computer B OR Computer A and Computer C to network, but
not all three at once. The third computer will not accept
the wireless network WEP key. The only way I've found to
bypass this is to disable wireless security.

Any ideas???