Error message when cron expression cannot be parsed is not understandable

6.0 r28692

I have setup a cron replication, and too fast copied pasted a cron expression from the provided examples, without removing the quotes. When I have clicked on "Save", I have got the following message: "An error has occured during the processing of your request".
We could also remove the quotes from the examples, as it is useless since we have refactored it into an html table.