same problem with you .. Take a look here
It's possible that the folder I copied
was corrupted somehow. So, I just
deleted it from my USB hard drive
after doing a Drive Check (with only
a File System Fix, from
properties->tools the Drive Check
button -- basically a checkdisk from
explorer in Vista). I had also copied
this folder to the Folder in Which MS
keeps the backup sets. Anyway, after
deleting it, I don't anymore get the
error 'An internal error occured while
enumerating backup sets'. Now I'm
restoring from my USB external drive
with no problem. Essentially, the
reason this problem occurs suddenly is
that something gets corrupted on the
Drive you restore to from