If a sketch feature (design step) is displayed with a red cross in the 3D history [3D History] there is an error. A specific error message then appears:

To display the wording of the error, click on the option Show error. [Show error...].. option in the context menu.

Example 1: Error in base extrude

A negative value had been chosen for the extrusion length.

Example 2: Error in the sketch

Edges cut or intersect themselves.