Try using Map clean up tools to get rid of the errors. If you created the contours using plines and there area areas that overlap, self interstect, etc... you will get an error. You will find that Map will clean all of those up for you quickly.
R10 - 2020 ACAD
2008 - 2020 Civil 3D
2014 - 2020 Plant 3D
2014 - 2020 Revit
V8i - V8i SS4 Microstation
Infraworks
2018-2020 Inventor
2020 Navisworks