I have been playing around with the different Anti-Virus products available and was testing out ESET Mail Security for Exchange and came across the following error that logs quite often:
While I did not notice anything happening with the transport service and mail was flowing as normal, it seems this is a bug in the application rather than an actual problem.
If I remove ESET from the server, the above error stops logging or if I disable the Transport Agent no error logs.
Hope it helps.