If there is invalid contact it will tell you in that window which features on which components are interfering.
If you have a thin model, you may need to refine your mesh. Go to your local initial mesh settings. There are 4 tabs, click the help button on each to learn what each option will do...
Try to use the Floworks "check geometry" tool. (FloWorks > Tools > Check Geometry, Check) It will tell you the volume of what it recognizes as fluid and solid. If it reports that you have 0 solid volume then you may have a problem. This tool should really be used on every model, especially in...
