Fiscal Year Start And End Date are not editable

Hello ..

I am new in using Dynamics AX 2012 , I am about Learning GL Setup  , 

I have faced a problem in creating my first fiscal calendar , when i create a new fiscal calendar it by default automatically creates first fiscal year at this fiscal calendar .

The problem is that when i try to set the first fiscal year start or end dates , but it is not editable ,  and the next month button of the calendar is dimmed as it shown in the attached image Image may be NSFW.
Clik here to view..

How can i fix this problem ?

Thanks .....