Random 'Artifact file not found' errors

Apologies for the vagueness of this but we, seemingly randomly, get the following error during our Build step across at least two of our plans:

DEBUG: Inheriting deployable (ID=0) from context.
DEBUG: Artifact "Project.SmokeTests" found (ApplicationId=80, ReleaseNumber=0.5, BuildNumber=51, DeployableId=0).
ERROR: Artifact file not found at expected path (D:\BuildMaster\Artifacts\A80\R525\B7615\Project.SmokeTests.zip). It may have been purged as part of a retention policy.

If we kick the build off again, it succeeds with no issues.

Incidence is pretty low (~1 in maybe 50 builds).

Any ideas what could cause this?

Product: BuildMaster
Version: 5.6.8

Well, the only code path that will yield that error is if System.IO reports that the file requested is not on disk. The most likely cause of that is that the file is not actually there at the time (obviously), but that might be because anti-virus quartanteed it, a file server didn't replicate it, or something?

So, I would try to find what might be causing that file not to be there. The only way that BuildMaster will delete a file (but not the record) is a retention policy.