You receive an error message which reads:
WinZip cannot open D:\data3.cab because it is not in the standard Microsoft CAB format (as defined in mid-1998). The "signature bytes" required by the Microsoft CAB specification are missing.
This error message may appear when cab file type is associated with WinZip. Try unchecking cab file association in WinZip options or uninstall WinZIP for the duration of The Witcher 2 installation.