This seems to be a new problem popping up more and more frequently.
We currently aren't sure how this is happening, or even why it is happening.
Let alone how to fix it.
Therefor, I would like to ask you what Operating System you are using (and possible service pack).
If you are using Vista, then try the compatibility tab of the setup.exe located on the disc, and set it to Windows XP SP2 or lower.