evernote for iphone having erratic synchronization errors with photonotes.

i'm using evernote for the iphone (latest version for the 3.0 os). when i create new photo notes on the iphone, i frequently get an error message dialog that says "Synchronization failed. Unknown Error u5." one error message appears for every note pending synchronization. i deleted the app and reinstalled it, which solved the problem for a few days and then the sync errors recurred. is this a known issue with a fix? if anyone could point me to documentation (i've looked without success), that'd be great.