I attempted to create a simple sine curve y=sin(x) using the equation driven curve.  I get an error that indicates that it can not be resolved and I get the following error message:

Warning Sketch1   The sketch has not been updated because solving it would result in invalid geometry (such as a zero-length line).  Consider :      o Deleting the invalid geometry.     

                     o Changing relations or dimensions to eliminate the invalid geometry.

It is the only line on the sketch.  I have used equation in the past and have never gotten this error message.  I don't know what I can do to resolve the problem.