When I last read anything about that error in Word 2007, it was caused by AV software apparently failing to unlock a file after scanning it. But that was a few years ago now. As I understand it, some AVs lock files and some don't, just as some other software doesn't need to lock files. If your H partition is an external drive, that might be a factor in this. To see if any other software is locking your file, search for Unlocker, install it, and use to view the processes that are locking a file when you next get this error. No need to use Unlocker to remove the lock or end the offending process if you don't want to mess with it; just use it to find out whether this is the cause. If it is, change your AV software.