After I applied the Technical Refresh updates to my Office 2007 Beta 2 installs, I started getting this error whenever I tried to open a file with an Office 2007 application (either by double-clicking within the Windows Explorer file list, or by opening the file from within the application):

The file Testing.docx is not available.

So I asked Uncles Google and Live and came up with the comments to Jensen Harris’ blog post about Office 2007 Beta 2 Technical Refresh. In it, a Phil Wright asks about this very same problem. In a comment immediately following is the answer. Apparently the Norton Antivirus Office Plugin is interfering, returning an error code on document scan, which Office then interprets as a virus detection. To fix it you can try to update Norton via Norton’s LiveUpdate (I tried, to no effect), or you can reduce your system’s overall security by disabling the Norton Office plugin. Instructions for older versions of Norton are available in Microsoft KB 329820. In Norton Internet Security 2006 (my version), I opened the Norton status window, then chose Options -> Norton Antivirus, and among the tabs found an option to disable the Office plugin.
This worked fine for me.