I had to reset my computer to factory defaults, in trying to reinstall my X3 upgrade I get this message about the time it starts to unpack part 3... "Fatal Error: This program has got corrupted internal data: it will exit. Please obtain a new copy." I've deleted and redownloaded and attempted to reinstall several times, same error... any ideas?

Try downloading from another browser. Chrome or Firefox for instance.

Verify the MD5 values via the installation page for all 4 files prior to the install. I use a free program called "FastSum" for this. It will verify the downloaded files are correct. You may potentially have an issue with the part one file.

Is the original version of X3 still working fine? 
You may have to think about re installing x3. 
Did you disable your AV while downloading? 
It is a good practice to just before you click the download icon, shut everything else down and set your computer to never not go into standby etc. 
I don't even touch it until it's over. 
 
 

I will try all of these and let you know how it goes.

I had this problem once before. I uninstalled and then ran a free registry cleaner (Jet Clean I think) before attempting the re-install. Everything worked fine.

Tried everything, so I'm not sure what worked, but something did... thanks everyone.

If you don't mind, please add 'Solved' to your subject line of the original post.
 
Thanks, 
 
Bob Bone