Lots of command line switches for v4. A good one: specifying the drive letter for virtual drive 0,1,2,or drive 3 (4th virtual drive).
DAEMON Tools could pop up a message saying "Drive letter not available" or if the user sends another command line switch -ignoreDriveLetterInUse then you silently ignore the error and don't change the drive letter. Another option would be a tray icon setting saying "warn about commandline or API errors" and the default setting would be to never warn about errors.
DAEMON Tools could pop up a message saying "Drive letter not available" or if the user sends another command line switch -ignoreDriveLetterInUse then you silently ignore the error and don't change the drive letter. Another option would be a tray icon setting saying "warn about commandline or API errors" and the default setting would be to never warn about errors.