So what gives with SyncToy 2.1 on Windows 7 64-bit? Last night I manually closed Outlook, then after it had exited cleanly I executed my folder sync. As mentioned previously (here, and here, and here) the sync command runs all my “active for sync” folder pairs in SyncToy 2.1, of which there are two. The first backs up c:\users\myname, and the second backs up the singly-rooted folder hierarchy in which I have stored all my stuff since 1987 or so.
I run this before I head upstairs for the night. Twice now I have come down the next morning and found Outlook sitting there with the message “The default storage file cannot be opened,” or something very similar to that. Also, and I had initially disregarded this as coincidence, when Sidebar restarted it only displayed one of three gadgets, and none of it’s windows would activate off of the desktop context menu. In both cases restarting solved the problems, but Outlook complained on restart that the PST file needed to be scanned.
The last point of interest: I keep my Outlook .PST file in that singly-rooted folder structure I mentioned above, not in the default location. Not sure what’s going on here, but I am beginning to think this one is SyncToy’s issue, not Outlook’s.