I have the same problem. I tried to click "reset my default keychain" though, and it said it couldn't obtain access to do that, then the login keychain disappeared totally. I had to do keychain first aid, which added a new empty login keychain, then I tried the "reset default" again, and the login keychain disappeared again.
I know how mine got broken: I forgot the password to get into my MacBook Pro, so I followed some sort of instructions to reset my Mac password.
I got back into the Mac, and everything was just as I left it, but now I'm getting non-stop requests like nross5's that Calendar agent, Mail agent, Safari, Local Items, etc. want to use login keychain.
I've tried doing keychain repair, changing the password, tried reseting to default as suggested by Dib, and I'm still getting these requests. Do you have any recommendations?
Thanks,
Mandy