Imagine an use case that a backup is performed and its target folder renamed or removed afterwards.
With next repository request (content activation, dms file download, whatever) Jackrabbit tries to resolve such content from that (nonexistent for him) path (log is attached). Perhaps we shouldn't let him store the backup related state at all so that he'll be looking for the content in repository again.

As a workaround it's enough to restart the server. If it's not possible, you need to keep the original backup file in the original path for a while.