At least one part is not connected to the structure. One way to find unconnected parts is in Workbench to drag a Modal analysis onto the Model cell of your Static Structural. Open the Model and in Mechanical, drag the Simply Supported and Remote Displacement constraints from Static Structural down to the Modal branch.Â Under Analysis Settings, increase the number of modes to 12.Â When you solve the Modal analysis, plot the displacement for all modes. I expect you will see the first 6 modes have a practically zero frequency. The displacement result will tell you the part that has the largest displacement and when you animate, you will see the loose part flying around. Add a connection between that part and the rest of the structure and rerun the Modal analysis. When all the loose parts are connected, Mode 1 will have a non-zero frequency.