Hi,
If you reopened a message after it got the error, it won't send again (since you're in control how, maybe you don't want to send anymore).
However, if you don't open the draft after the error, it should be sent with the next sync....
You can tell by looking at the drafts message list: there is a per message "scheduled to send" icon indicator there.
( I just double-checked, too, so if you're still having this issue, please contact me at kmansoft / gmail )