Dreamweaver CS4 file sync errors: file in use by another process

Over the past few weeks some file syncing errors suddenly occurred where files were locked ‘in use by another process’. I tried all the usual culprits, numerous reboots, turning off every unwanted program, safe mode, checking Windows’ services, using Process Explorer but nothing cured this ‘file being used by another process’ error and my web sites risked getting into a mess.

Well I finally found the culprit after two weeks of problems! More details...