First: Make sure the WEP key you're using is the same characters, in the same format: Some devices ask for the WEP key in HEX characters, some will automatically convert the ASCII text characters into HEX.
So, if you've added a key like:01 02 03 04 ....into the symbol (symbol thinks it's HEX and treats it as a number) and the same key into the Cisco (with the bullet checked as "ASCII") then the WEPs don't match because the "01" "02" "03" etc are being converted into the HEX equivelent of the ASCII representation.
Wireless analyzer software is your only option there. You can check out CommView (tamos.com) or AiroPeek (wildpackets.com), or AirMagnet (airmagent.com).
CommView and AiroPeek Laptop SE are pretty good deals (~hundreds of dollars versus Thousands of dollars).
All three have download demo software that will provide limited functionality and / or time-bombed.
Check 'em out and see which one fits your needs best.
Good Luck
Scott