by Ken Task.
Yes, you can manually remove anything in moodledata/temp/backup/ that's not an active backup in progress of building.
Is a directory *like*:
d45986723ed5486d32e2784696ed45ef
present?
If so, what's in it? If you see a .mbz file there, the backup did complete but, for some reason, can't *copy* the .mbz to it's destination for some reason. But, one can *mv* it to a destination manually ... yeah, I know you want it to work, if you 'mv' you have at least one good backup.
Also, might get a clue about quizzes by looking at questions.xml if present.
'SoS', Ken