Share your experience!
You can move some of your apps to internal.Settings-apps-all-downloaded,there are all your apps downloaded and installed.
But how much free space do you have in downloaded (phone memory)?
as specified in the original post, over 400mb of 2gb.
Could you perform a software repair?
Yes,that is what it involves.If not,you can stop by a sony service :
http://www.sonymobile.com/global-en/support/contact-us/