Faced the same problem as given in this earlier post, with the schedule csv/email creating script complaining that SIGNATURE TUNE not found, "PROGRAM NOT FINALISED". The solution is to just search for entries in the playlist table where timestamp is 2011-08-16 06:30:00+05:30 (or whatever date). This can occur at midnight also - as PB pointed out, a bug in the script changes a timestamp of 2011-08-16 00:00:00+05:30
to 2011-08-16 06:30:00+05:30 during the import process. So, verify if the correct timestamp should be 00:00:00+05:30 and then edit the entry manually from 06:30:00+05:30 to 00:00:00+05:30 .
The point to be noted is that the problematic entry may not be adjacent to the actual 06:30 signature tune file, it could be at midnight also.