Try this test to check if root working properly
Install Android Terminal Emulator from Play Store
From terminal emulator type "su" without quotes
Check if any superuser app prompt your answer to grant it using root privileges
If you're asked, then your root working properly.
Now type "mount -o remount,rw /system". Is it still permission denied? If so, so your problem is Sony RIC. If it's success, then your /system can be wrote now. Try to copy something to /system now. Check if the permission still denied or granted.
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