Are you allowing R scripts to run? It seems like this is an error you'd get if R/Python is disabled. I just ran it with Tableau 9.3, 10.1 and 10.0 and didn't get any red pills for Curve Fit and it rendered fine.
So, I guess it was an expectation thing. I thought I'd download your workbook. Open it, and it would simply work. It sounds like I have to install R and/or Python for it to work. Wasn't aware. Sorry for the misunderstanding.