Sinumerik Alarm 109002 No switchover: Target PLC occupied, try again
MMC would like to go online to this NCU. MMC has called the target PLC and is awaiting acknowledgement. No acknowlegdement for MMC since MMC parameter interface in DB19 is assigned by another MMC.
Repeat the operation at a later point in time, as the MMC parameter interface in DB19 is only temporarily occupied.
- Siemens Diagnostics Guide by Siemens