[quote=ImANargleHunter]
You're probably signed in on your other account. My sister does that all the time, because she'll leave her skype singed in on the home account and will try to sign in on the office account.
[/quote]

No, I only have one I ever use. It's a consistent problem - I can't log back in once I've logged out, even if it's immediately afterwards. Plus, how would I be signed in when I'd only just installed Skype again?