Moving apk to system/app. Operation failed
Most devices have the system partition mounted as read-only. You need to remount the partition with write access so that you can modify the files.

This free app should work. Other utilities such as ES File Explorer and Titanium Backup also have the ability to remount the system partition as writeable.

Alternatively, you can use a Terminal Emulator or ADB to run the following command, which should remount the volume as well.

su
mount -o remount,rw /system /system

After the volume is mounted as read/write, you can go ahead and move the app over. The volume will remain read/write until you reboot the device, at which time it will revert to read-only.