SEP 14 MP2 postsession callback error

Environment

Windows 7 Professional SP1 64 bit

SEP 14 MP2 UNMANAGED clients

Issue - intermittent LiveUpdate error "An update for SONAR Definitions from LiveUpdate failed to install.  Error"  Postsession callback failed (208).

We are download updates from the Symantec LiveUpdate server.  No SEPM is involved.

Anyone know what a Postsession callback failure (208) is?  Why do they happen?  What is the fix?

We can manually run LiveUpdate immediately after the postsesson callback error and the SONAR update is successful.

We are assuming that there is something wrong with the SONAR update package.  We may go for days with successful SONAR updates and then have a failure.

Don't tell us to Cleanwipe and reinstall or run SymHelp or whatever.   We're looking for an answer as to what and why a postsession callback failure occurs.