I'm running version 2012 with the service pack installed and it works fine when I click on an arc. Not the OP's arc but one I drew.
I have the same issue in 2011, with the service packs installed. To make it work, change the "Fixed .." from Delta to Radius. Then input the info you want and see if it doesn't work. Aggravating, but it works.
Could you please elaborate a bit more how to get the dialogue box that you are showing in the screenshot (curve calculator)?
From the "home" tab, under the "draw" panel last on on the list.
Many thanks Bruce. I got it