SMART is the disks internal tests to determine it's own health. It's also what is likely making its read only. You can get software to read this smart data, it gives you a clue about the drive health. With it being external, try changing the USB cable.
Discussion
Thank You.. I already changed the USB cable. How do I Access this data on Linux? I will check what fsck will tell me, later. At the Moment I copy down the Data, but it is still on rw mode. Since about 2 hours.