** ERROR 99787 ** Orientation of part element element number is in reversed direction. Use mesh tools to orient the element the other way and run the analysis again.
The orientation of the part element is in the reversed direction, meaning that the top and bottom sides of the element are different from the rest of the elements in the model.
Clicking (Mesh > Orient All) to orient the elements automatically. If further elements still need orienting, click (Mesh > Mesh Tools > Orient Elements) and manually orient them. Then, re-run the analysis.