Doh! Twitter goof-up.
Okay, so I just found out that because I 'secured' my twitter-updates, Twitter's API was requesting log-in information from anyone trying to look at my blog (since the tweets feed to my blog)
For those of you who don't have a twitter account, or anyone weirded out by my blog asking for account information - my apologies. I've since unlocked my updates and I'll deal with twit-bots for the sake of open access to my site.
Of course, its not too late. You can always just join twitter.