Hello bhkolts,
I recently had the exact same problem with a Toshiba laptop that I purchased for one of my daughters. I have performed the system image process on 3 other laptops, all running Windows 7 Home Premium 64 bit, with no problem during the last 4 months. My personal laptop is also a Toshiba; the other two laptops purchased for my wife and our middle daughter, are made by Gateway(Acer). Thus far, in my case, the problem was intermittent.
The weirdest part of the incident that I encountered is that Windows actually advised that the process was complete but when attempting to safely remove the dvd and close the window, I was then advised that the process was not complete and required another disk in order to transfer the remaining 4mbs! lol Which became even more humorous when I attempted to safely remove the disk and was advised that doing so would end the imaging process.
When I checked the properties of the dvd, I was very surprised to see that is was listed as completely full and expected it to be corrupted for certain. To my surprise it was readable, but not a complete image; nor functional.
After one more attempt with the same result I began troubleshooting. I will spare the details and jump to the solution; in my case the culprit was the device's driver. I downloaded the update from the Toshiba website with my computer and transferred it but didn't solve the issue. I Un-installed the device, rebooted, re-installed the device, and rebooted; no change.I used the Toshiba recovery software instead and had no problem. Following the philosophy of Occam's Razor (rarely works-lol) I re-installed the OS using the Toshiba recovery disks. Problem fixed!
A few days later the drive began acting up and would only allow my daughter to burn files in the mastered format. When I finally paid enough attention while on the Toshiba support site I noticed the driver was listed under "known concerns" with the status of "developing solution". With the next update the problems have disappeared.
I agree with one of the posts above in regards to the different levels of application availability between the various Window's 7 versions but believe that if Windows 7 Home Premium 64 bit is the culprit in your case, that it is most likely service related. I have noticed that services set to "manual" don't start up as consistently as within Windows Vista or XP. I have also witnessed on occasion that a services set to "automatic", will mysteriously stop running with no dependency issues or other explanation. Volume shadow copy is among those in which I've noticed behave in this illogical manner.
I personally tend to over complicate issues while troubleshooting; adding the philosophy of Occam's Razor to this equation, would lead me to swap the drive as the next step if you can not locate a newer version of the device's driver and are unable to catch a needed Window's service sleeping on the job.
Good luck!