iCloud storage query
I have 20gb of iCloud storage of which I have used 4gb. However when trying to automatically transfer photos from my Mac to my iPad I am told that "this library exceeds your available iCloud storage" and that I must upgrade my storage plan. It doesn't make sense as I keep being told that I still have 15.9GB available.
Please explain. Thanks
iMac, Mac OS X (10.0.x)