Normally it will read “File is missing in schedule, Error: 2”
Example:
You create a schedule with 3 messages. The message names are Wednesday, Thursday and Friday.
You then save you schedule but realize you need to make a change to message named Wednesday.
When saved the file you decided to also change the file name to Monday.
You add the new message file Monday to your schedule.
To not confuse the two files (Monday and Wednesday) you then delete the old message file named Wednesday (but you did not remove the Wednesday message from your schedule).
When you send your schedule to the sign, the sign tries to play the message file Wednesday, but it cannot find that message file (because you deleted that file).