I use TCGPlayer to scan my cards and export to a CSV file. If I don't have foils in the CSV it imports fine. But with foils I get NaN under Foil count. I also tried to use UrzaGatherer format and it still get the same problem.
To see this working, head to your live site.
Just got home from work. I fixed this by deleting unused columns. Then moving and renaming quantity to Count and foils to Foils count. All the normal's changed to 0 and all foils changed to the count number I have. Very easy to change.
Can you share a simple example of a csv that does not work?