CRC error

when i mounted an image of my neverwinternights cd3 in alcohol windows reported a CRC error when the installer tried to copy a file off the virtual drive but when i burt the image to a cd rw i could copy the file:confused:
I’ve tried this with alcohol 120% 1.3.4 (1108) and the latest 1.3.5.(1112) with the same results. Does anybody know why this happends?