I recently downladed the Autocad 2015 student package and started working on a project of mine. I have a polygon and want to bump out the faces by exactly the same value. I am using the Arc command end,end,radius to do this. I set one end at the vertices of the 2 sides and then set the adjacent corner / end. The command line ask for the radius and after I have input the radius dimension, I get the error message of "invalid 2D point". This occured originally while trying to do the last side. I went back and removed the "bump out" on all the sides came back to the one side that I could not do as my starting point and I still get the same error message.
The command is telling you that it is not possible to create an arc of that radius that passes through those points.
If you post a drawing and the data you are using someone could probably tell you exactly why it's not working.