RETAIL (PHYSICAL DISC) COPIES:
This kind of error happens when your disc drive cannot read the file on the disc. To fix this, please:
a) copy all the installer files from all the discs onto your hard drive, and install from there, or
b) use the code printed on the back of your booklet, to redeem the game on GOG.com, here: www.gog.com/redeem/
GOG.COM DIGITAL INSTALLER VERSIONS
Make sure that you have at least 30 GB of space available on drive C:, or that you do not install the game onto drive C:. Otherwise you might run out of space during the installation, and it will fail.