Error in the midle of copying disc

Hello,

I use laptop with eksternal DVDwriter (LG super multi 22X <NEW>) and USB 2.0 to SATA IDE Cable <NEW>.
When I burn a DVD with Nero or other copying sofrware sometime succesfuly but sometime fail in the midle,
nero error massage say "no divece avelable G:" my DVDwriter drive in G:.
If I burn with my internal DVDwriter (buld in laptop) 100% succesfylly.
Before never happen so I thing the problem is DVDwriter and USB Cable so I change it with a new one and
reinstall nero but the same problem still appear.

My laptop have 3 usb port, USB Cable compatible with all of them but for mouse just one port the other two
can't be used.Is this problem connected?

What is the problem can you help me?

Thank You.