Two identically looking documents print differently?

I load up a document to print and it looks fine, but when I print it, it has a two and a half inch strip where black ink isn't printed. There are 50 or so files that I created a month ago that now have this error. Re-exporting the document seems to fix this problem. The two files look identical in Acrobat, but the one prints with the error. Any idea as to what is going on? Is this some sort of file corruption?