Burner works better external?

I have been having a problem with my LITEON LH-18a1. I have used it internally for almost a year. I thought that I got a lot of I/O errors. I would get read failures, write failures. I had an external usb to ide not used, so I tried it it works without problem for the read and write. Is it possible that the IDE cable, or the sharing of the cable was the problems? I have three hds and a burner so sharing seemed the only option. If Burner and a hd on a cable is the problem what should I do instead? raid card?

Any thoughts would be great. THANKS