Across the internet, you are the lead investigator into this issue.
Nearly all discussions are duplicates of your same thread. To date, no
one has stepped in yet with the final answer. You have not posted a
followup to indicate that you have found the answer either. The URL I
found that has the most replies to your thread is:
'Vista Complete PC Backup error 0x80780048'
Today, I ran into this same issue on my 64-bit version of Vista.
Apparently, the oldest backup has been removed, but it looks like the
Backup and Restore Center still thinks that it hasn't, because it is
still displaying the oldest backup date, which doesn't appear on the
external backup drive when I open it.
Shawn, who I believe owns this Vistax64.com website forum, helped me
solve my last Vista problem. I was hoping he would have already had a
tutorial or final solution for this problem, but apparently he does not.
Hopefully, he can solve this problem too. That is why I chose this forum
to reply to your thread.
Could either one of you please follow up.