You're going to have to give us a lot more information than that.
What's your set up?
I'll go out on a limb and guess that you're trying to install Mach3 on a 64 bit operating system and running a parrallel port BOB.
Until we know more, we are just clutching at straws.
"Mach3 Minimum Recommended Requirements:
Requirements if using the parallel port for machine control:
Desktop PC (Laptops are not supported) with at least one parallel port
32-bit version of Windows 2000, Windows XP, Windows Vista, or Windows 7 (64-bit versions will not work)
1Ghz CPU
512MB RAM
Non-integrated Video Card with 32MB RAM(Large G-code files, especially 3D files will require a video card with 512MB RAM or higher)
Requirements if using an external motion device for machine control:
An appropriate external motion controller (options can be found on the Plugins page)
Desktop or Laptop with Windows 2000, Windows XP, Windows Vista, Windows 7, or Windows 8
1Ghz CPU
512MB RAM
Video Card with 32MB RAM(Large G-code files, especially 3D files will require a video card with 512MB RAM or higher)"