Well, i would change the file you are looking for to
\\serverName\backups\backupFileName_SITE.XML
<file:///\\serverName\backups\backupFileName_SITE.XML>
I take it when you are pointing spsbackup at the backup you are
selecting the xml file is what I am saying ?
Also .... dumb as it sounds, you have checked the files are there ?
Finally, have you checked the permissions on the folder the files reside
in
Other than that, not a clue