"The nudge distance you entered is invalid. It must be a positive non-zero value."

I seem to get this message every time I change units.

For instance, I was working in inches and I wanted to scale something to an exact pixel size. I go into Options and change the Units to Pixels. Ok.

"The nudge distance you entered is invalid. "

I look at the Nudge setting and it's 1px

So what's the problem?