Even though fill surface option has tangent condition with already existing surface there is a contradictory warning sign. What is the reason for that?
This usually happens when a Fill or Boundary surface is set tangent or c2 to more than one surface or edge. It usually happens because you're asking the software to do something contradictory. For example, if you have two adjacent non-tangent surfaces, and try to make a patch that is tangent to both of them, you will probably get this error, and the resulting feature may be ok, or partially ok, depending on your standards. For example, if you have a pyramid with the top cut off, and want to round off the top with a Fill surface, the adjacent sides of the pyramid cannot form a surface that maintains tangency to each and its own internal integrity (there will be a zero radius corner). So the surface meets your requirements everywhere except the sharp corner. That's why the warning message is a little indecisive with the word "may".
The result is ugly
If you add fillets to the edges, all adjacent faces are now tangent. You might still get the error, but at least the result looks more like what you probably intended;
Thanks for the explanation.
Retrieving data ...