When generating a diagnostics packege from the Symantec Messaging Gateawy (SMG) control center via the Administration->Utilities->Diagnostics page using the SCP protocol the first attempt to transfer the diagnostics file to the configured host fails and an error is logged to the BrightmailLog.log file.
A second attempt to generate the diagnostics file does not result in this failure and the diagnostics file is transferred as expected.
Workaround
A second attempt to generate the diagnostics file using the same parameters and destination host will not be affected by this issue.