Oh dear.
The password should be saved in your keychain. To view the keychain:
Open the Applications/Utilities folder (click Finder in the task bar, then hit Apple+Shift+U).
Run Keychain Access
Scroll down to the name of your network - it should say "Airport network password" in the Kind column.
Click the "Show Password" checkbox. It will prompt you for your password (the user's login password you used to log in to OS X) and then it should show you the password you've stored. Is it the right one? If so, click Access Control and check that "Internet Connect' is on the list of applications that is allowed to access this keychain item.
I have a sneaky feeling it won't be listed at all - hence your problem, but take a look before we go any further.
By the way, what version of OS X are you running? (Click the Apple, top right, and choose About This Mac)