There are a bunch of people around the ‘net posting about the “u11” sync error in Evernote on iPhone (perhaps elsewhere). If you are experiencing this problem, you have HTML embedded in your most recent change/note that is trying to synchronize (perhaps through a copy/paste, etc). Evernote doesn’t support syncing embedded HTML. You can identify this by the blue highlight that such text will have when you view the note.
To solve the problem, either
(1) Delete the note from both your phone and/or your account
(1) Use the Evernote app on the phone to log into Evernote
(2) Turn off Wi-Fi and 3G and go to a no signal area so that Evernote won’t try to synchronize
(3) Open Evernote and open the affected note for editing
(4) Remove the portion of the note containing embedded HTML and/or links
(5) Turn networking back on and synchronize
Basically, don’t post anything with HTML into Evernote. It’s a plaintext-only application/solution.