I'm seeing reports from people who say they're unable to send DMs to someone who is already following them.
For example, @fiercehugs has a tweet that mentions this:
fiercehugs: @twitter Having DM problems. @yoga_mama & I follow each other & can only DM using msg link from other's web page; not from our own DM page
12:32 PM October 09, 2008 from web
@royblumenthal's recent tweets also mention the same problem:
royblumenthal: @mediacoach Just tried to send you a direct message, and it says you're not following me. Which is odd. Will you refollow? Thanks, mon.
42 minutes ago from web in reply to MediaCoach
royblumenthal: @mediacoach It's some kind of Twitter bollocksing. You'll need to unfollow, then follow again. It simply refuses to let me send you a Direct
25 minutes ago from web in reply to MediaCoach
royblumenthal: Is anyone experiencing Twitter hassles with trying to send direct messages? I get 'you must be followed by this person' errors. You?
20 minutes ago from web
royblumenthal: I can send directs from a person's profile page. But nowhere else.
19 minutes ago from web
A look through Twitter Search easily turns up a few more people :
mzamp01: @LiveCrunch For some reason I can't DM some of my Followers...
about 7 hours ago from web
PinkOliveFamily : Dear @twitter - I'm still having prob with DMs (although I can clearly see that both following each other) - second commt today
about 13 hours ago