Could be that your object is really tiny in the scene, and therefore even small chamfer values create huge changes. You could try scaling the model up by about 1000% (and remember to Reset XForm - it's in the Utilities panel, if you can't find it, press F1 and look it up in the help)... then try chamfering again. Also, if…
Still playing with it, I think I discovered the problem. I believe the scale of my object was too small, and as such, any numeric entry greater than .01 mm was larger than distance between the two adjacent loops. Aside from that, is there any way of adjusting the "fineness" of the cursor? I suppose I could blow the object…