It sounds like you're on the right track using a repeat interval with "until". For example, the following will create a task that will occur on the 5 dates you indicated:

The Contract ^August 15 *every 1 month until December 15

It sounds like you may being seeing the task repeating past its end date in your calendar, is that right? This is because the iCalendar feed does not include an end date for the recurrence of the task, so it will show on your calendar indefinitely. Once all the occurrences of the task are completed or deleted, it should disappear from your calendar.

Hope that helps!

Oke Brandan thks, so the due date of the contract has to be the first reminder, not the end of the contract ?

Correct. At the time you create the task, the due date should be the date of the first reminder. When you complete this task, the next occurrence in the series will be created based on the Repeat property and it will have a different due date.

The "until" portion of the Repeat property indicates when you want to receive the last reminder, so this could be the end of the contract.

Hope that helps!