even though there should be plenty of space available http://imgur.com/WAjmIwC
It won't even let him upload screenshots to imgur http://imgur.com/80Ihwnb
He bought it a few months ago, it's been having this problem since shortly after he bought it, it's fully updated and running Android 4.4.4 http://imgur.com/98UAlDF
When trying to install programs, such as the very small DiskUsage app, it gives the insufficient space error even if he's just cleared app caches and uninstalled apps, which should definitely have cleared enough space to fit it.
What can we try to fix this? He'd prefer to avoid doing anything too complicated such as rooting or installing custom ROMs.