Why does defrag mess up some games...??

I've had my rig for almost 18 months and only 2 games ever got messed up by defragging.

One was NWN 2

And now Dead Space..

No matter how many times I reinstalled NWN 2 it would either crash on load up or if it did load when I tried to load a save game....if I did a defrag.

I played all of NWN 2 without defragging and it was just fine..

I installed Dead Space today and while waiting for the sun to go down and cut the glare I defragged.

Then when I went to restart the game it crashed ( I had played it for a couple of hours earlier with no problems ) Retried and it loaded but now it crashes in the same spot every time.

The error message says a file is missing...( I was way past the point where it crashed in my earlier play...way past )

So what gives..?

Now I have to re D/L it from Gamestop.....so much for saving the shipping charge. It's times like this I wish I had the physical disc.

Live and learn...it's only 8 hours...

I have never gotten NWN2 to install right. Every time I try it cmesses up before the install finishes. Anyways, WoW I didn't know Gamestop put up there PC games for download.threepac81

They started a couple of months ago...

Thats too bad not getting to install....decent game.

I should clarify it did not crash once in my first play..only after I defragged.