Case of the unexplained

I was doing a routine software install on a few machines the other day and the last one I came to was giving me this type of error:

I fired up process explorer and checked the stack for the process but couldn't see anything amiss. I tried rebooting, disabling the anti virus but nothing and then I remembered "When in doubt run process monitor".. . so I did and here is what I saw:

I saw loads of files in a folder in a random users profile being hit by this executable for some strange reason :-\
So... I browsed to the folder myself and found that there were LOADS of files and I mean LOADS and the last one this executable hit was no where near the end of the file structure.
So it seemed that the deep and complex file structure was stopping the installation. I tried to rename the folder but it wouldn't let me, cut and paste to another drive it wouldn't let me so I moved it temporarily inside the windows folder as I thought surely this installer wouldn't try to enumerate the contents of the entire drive.
I then re-ran the installer with this folder now located in C:\windows and lo-and-behold it worked!
Thank god Mark Russinovich for procmon!