Dang! Fast fingers, guys!
But, no. Forcing it to be an integer does not help. I tried that earlier, with no luck.
That error shows up somewhere in the depths of the ESRI web as an Internal Geometry Error, or something like that. I played around with some of the vertices and found a single vertex that, if moved, it would run fine. See attached image. This is a tiny, 1-meter notch on one edge. One of many similar vertices. If I move the vertex and straiten out the edge, it runs fine. There is no way that this little spot should cause a buffer to fail! It runs at just about any buffer distance, integer or floating, except for right at or around 5 miles.
And there is no way that the user can or should have to go in and find the one little vertex that is causing problems. This is the tail end of a long data processing routine, and it works on 99.9999 percent of the polygons.
-T