This usually follows event 15007, and if so you will find more info about the cause there. It can mean that CRS indexed a file for replication on first pass but the file was renamed or deleted before it could be replicated. A common cause is that the file was open for exclusive access by another process. Check also that the CRS job runs with necessary privileges to read the file.
From Microsoft: Meaning: A file in the source directory on the local machine could not be opened.
Cause: File may be held open exclusively by another application. Recommendation: Free up the file and try again.
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