When receiving message ‘STC failure occurred mid transfer. – Final error (-5 Access is denied.)’ this is related to TrendMicro affecting the Datto client. To resolve this, use the instructions below:
a.  Go to the TrendMicro Admin Console.
Click on Agents > Agent Management > Locate the hostname in question > Right Click > Settings > Device Control Settings > Uncheck Enable Device Control on both Internal and External Agents tabs.

b. Then, on the server hit on Update Now via the TrendMicro tray icon.