AutoCAD Inventor :: An Error Occurred While Creating Finite Element Mesh

we've made a part from an assembly and put the stress analysis to the test. Unfortunately the analysis doesn't complete it's run, because of an error:

"An error occurred while creating the finite element mesh. The cause may be invalid geometry or features that are extremely small in comparison to the overall dimensions of the part. To fix the problem, please suppress those problematic features or use standard meshing method."

We can't change the thickness of the sheet-metal, because it's a model which comes from a supplier with a different cad-program. And supressing any features isn't possible, because it's a base-solid.

But where can we change it to the standard meshing methode? The program is recently re-installed on my computer, the settings haven't changed since it's been installed. We can't find the feature.