Comment 1 for bug 419471

This happens when you create a one-time task in gnome-schedule 2.0.2 and try to open it in 2.1.0. There is a bug in the parser of the data files.

This has been fixed in upstream and will be included in the next minor release; to manually delete your old tasks. Do in the terminal:

$ atq # to display all tasks, the first number is the job id
$ atd [number] # on all the numbers that showed up in atq

go to the gnome-schedule data dir:
$ cd ~/.gnome/gnome-schedule/at/
$ rm * # delete all files in the directory

- gaute