To tackle this problem, try creating the plist using a plain text editor. Perhaps TextEdit is showing some odd problem, so for now use a Terminal-based editor like pico/nano. Here's how to do it:
1. Delete the current Launch Agent file you created.
2. Open the Terminal and run the following command:
3. Copy and paste the plist contents from my latest post (above this one) to the Terminal.
4. Press Control-O followed by Control-X to save and exit (not Command).
When done, log out and back in to activate the agent, or you can use the following commands to load, start, and unload it, respectively (for testing purposes):
launchctl load ~/Library/LaunchAgents/com.jamesrydings.AutoBackup.plist
launchctl start com.jamesrydings.AutoBackup.plist
launchctl unload ~/Library/LaunchAgents/com.jamesrydings.AutoBackup.plist
Great! Glad it's helped. If you find yourself doing more of these type of edits and customizations, you might benefit from using a more robust text editor. One I recommend is the free TextWrangler: http://www.barebones.com/products/textwrangler/