Serious Disk Error?

I work on a travel demand model.  The model I use starts at 300 MB and throughout the run process, the size balloons to 2.5 GB from all the data that is created and calculated.

And I can make it go larger by producing some *REALLY* big reports.  There was one I produced that was 800 MB of plain text.  When opening it in Notepad, it would take forever as Notepad read the entire file.  I thought that maybe Word would read it progressively and allow me to look at the the file while it was loading.  I was wrong.  Word instead of telling me that the file was too big, it told me: