Offset Surface operator, Offset surface failed- some sub-elements are erroneous

[Micho]

"Some sub-elements are erroneous" error message occurs while offseting a surface. Can anyone tell me why is it so?
View attachment 2060
Before I click preview there is offset surface operator pointing at the corner:
View attachment 2061
Any tips how to avoid the problem? Thank You
Offsetting of smaller value do help, but this is not what I want to obtain

 

[MrCATIA]

(sorry Micho for the delay - I just noticed your question)

The pictures are too small to read, but I think I've run into this problem before.

This is a common error when offsetting a surface; somewhere on the surface the radius of curvature is smaller than the offset distance. This causes the offset to "kink back" on itself. The second picture shows an arrow pointing to the lower-right side of the surface where the problem is.

You already said you cannot use a smaller offset value; but you do have some options, including:
a. modify the original surface by making the increasing the curvature at the problem area
b. Spilt the surface to cut-off the lower-right section, and offset the remaining surface. Then make a Fill surface using the edge of the offset and an edge along the bottom.