I have some curves here I want to make a planar cover surface from but viacad is not letting me. It gives the message " Invalid wireframe for cover surface!". There are no gaps or overlaps. All curves are planar.

Sorry Tim, I meant to do that. I since joined all the curves and then converted them back to arcs and that seemed to work.

The curves were generated by exploding curves off other geometry and then projected to the workplane. I couldn't get the curves to join right using the connect curve command. I often connect and trim curves using the fillet command and setting the size to "0".