Hi Bob,
I'm also using V21 PP. The first time I use Help it gives me the option of Online or Offline (with Online pre-selected). I've found that if it gets into the state of Online, then I can't find an option for Offline, unless I close and re-open the drawing.
I suspect that your error message is the result of using 2D shapes that are not closed. A shape can appear to have no gaps in its border, but still not be closed in the TCAD sense – it will appear to TCAD to be a series of lines/polyline/arcs etc. Use the Join Polyline tool to join them together (if you can't find its icon, look in the Modify pulldown).
Another little gotcher is when the shapes are closed but are on different workplanes. This is a strange feecher of TCAD where entities appear to be co-planar to the workplane but TCAD insists they are not. If this happens (and it can even happen when you are working entirely in 2D mode), switch to 3D mode, select the entities, then use Modify|Place on Workplane. You can then switch back to 2D if you like, but I normally keep in 3D mode.