I am using DVD Decryptor with Windows Vista. Sometimes I will get a message saying I/O communications loss and then my computer will not recognize my CD Drive. This is also accompanied by a message saying the DVD was unable to Download. I am not sure what to do about this and if it is the program I am using or maybe a computer problem, though it only does this during DVD downloads.
I’m not sure that your meaning of “Download”… Though, if you are using DVD Decrypter for ripping DVD (Movies with copy protection), try DVDFab (free). If you are using it for burning, try ImgBurn (free).
I found that DVD Decrypter "captures" the DVD drive and won't release it; thats why the computer can't see it. You will need to reboot the computer (remove the dvd as it starts up again) and start again clean.