Rsync mkstemp failed: Invalid argument (22) with USB flash drive

I use "Back In Time" which is nothing more than a front end GUI to rsync version 3.0.9 protocol version 30. I'm running ubuntu 12.04.

My backup device is a locally mounted USB flash stick/drive formatted as ext2.

It gives me numerous errors similar to the following…

[E] Error: rsync: mkstemp
"/media/apb/0543d632-d24b-4b4e-8ca8-56d22c19e62f/backintime/myhost.mydomain.com/root/4/new_snapshot/backup/home/apb/Documents/7uzyrwsy.default-20131026-1639/Mail/pop-server.bak.rr-8.com/.Sent.msf.RZMdLy"
failed: Invalid argument (22)

The command line that Back in Time uses to call rsync:

[I] rsync -rtDH --links --no-p --no-g --no-o  --delete --delete-excluded  -v  
--chmod=Du+wx  --exclude="/media/apb/0543d632-d24b-4b4e-8ca8-56d22c19e62f" 
--exclude="/root/.local/share/backintime" --exclude="/tmp/backintime" 
--include="/home/apb/asterisk/" --include="/home/apb/" --include="/home/" 
--include="/home/apb/Documents/" --include="/home/apb/Linux-Centos/" 
--exclude=".gvfs" --exclude=".cache*" --exclude="[Cc]ache*" 
--exclude=".thumbnails*" --exclude="[Tt]rash*" --exclude="*.backup*" 
--exclude="*~" --exclude="/root/Ubuntu One" --exclude=".dropbox*" 
--exclude="/proc/*" --exclude="/sys/*" --exclude="/dev/*" --exclude="/run/*" 
--include="/home/apb/asterisk/**" --include="/home/apb/Documents/**" 
--include="/home/apb/Linux-Centos/**" --exclude="*" / "/media/apb/0543d632-d24b-4b4e-8ca8-56d22c19e62f/backintime/myhost.mydomain.com/root/4/new_snapshot/backup/"

Any ideas as to what's causing the failure, and better yet… how to fix it?