[Zope] DateTime and propertysheets

Hello, I have created a Product with a ZClass. The ZClass has a propertysheet with a date property. When creating an instance of this product I try to call the manage_editProperties method and modify the value of another non date property and I receive an Invalid Date-Time String. Now, I am not attempting to modify a date property but am still getting this error whenever I tried to change a value on the same propertysheet as a date property. If I try to change the date value to a valid date time value, I still receive the same error. Thanks