If you're getting a lot of zero byte downloads, it is a problem in the last few hours on various Google servers worldwide.
See here for the status:
http://code.google.com/apis/documents/forum.html?place=topic%2Fgoogle-documents-list-api%2FKXNyYCO2rsA%2Fdiscussion
This is causing problems for users who sync across multiple PCs.
Until it fixed, I recommend that you close or pause Syncdocs to avoid possible file corruption if Google has hassles coming back online.