Any known hardware/software conflicts with CR?

I have a VB.NET 2003 app using CR viewer for reports. I have one user that gets the "Object reference not set to an instance of an object" error when opening a report in CR viewer on two of their PC's. Their other PC works just fine. I have copied the Access DB to my three test PC's and it works without a problem on all three. I have even pulled their harddrive and stuck it in my test PC and it will work without the error. That leads me to believe that it's something with the PC. Are there any known conflicts with hardware or even software? Any help would be great!!!!

Thanks,
Joe