How can I stop Hootsuite from trying to send this failing message? So I try to send a tweet from hootsuite about this really nice beer I had. It was a nice beer, and a nice tweet, and nothing weird about it at the time.

The message send failed -- see screenshot, below.

The message cannot be found in hootsuite --  the message doesn't appear in my twitter feed, nor in "sent messages" (of course) -- the "Pending" tab is empty.

The message send KEEPS failing -- even though I've posted other messages from Hootsuite to Twitter since then. The message keeps trying to resend (and fail) every few minutes [no idea of actual frequency, but if I dismiss the message, it reappears sooner or later].
Have you tried clearing the data for the app?  Or uninstalling then reinstalling?  Or does Hootsuite cache unsent/failed tweets to the cloud?