Start with details
What Photo software and OS are you using - You posted in the Photos for Mac forum but reference iPhotos (which is not even a program - there is Photos and iPhoto - no iPhotos )
What disk is full? Where is your Photos or iPhoto library located? What exactly does an iDisk have to do with this? Have you emptied the Photos recently deleted album or the iPhoto trash and system trash?
How much free space do you have on your main hard drive (in the finder right click on it an get info) - If your library i son a i=different drive how much free space does it have and what format is it (in the finder right click on it an get info)
LN