Without being entirley sure why your animation doesn't rotate ... by slightly tilting the image in the final frame I have managed to get it to do a full circle. I think DP just needs a bit of help to decide which way the object is to turn.
It has shown me that the settings I used on a previously successful project (which I used here) are not generic settings. It must be to do with the object dimensions. There must be a mathematical formula to determine these settings!
I think DP just needs a bit of help to decide which way the object is to turn.
You can give it that help by selecting the object and ticking (or unticking) the 'Clockwise Rotation' checkbox on the Easing tab. When I load your file I find the checkbox in an in-between state with a solid box — I don't know how or why it got into that state!