To help resolve this issue, it would be useful if you could answer the following -
- Which version of the software are you using?
- Are you able to provide a screenshot or description of the model that you are trying to analyse? - does it include Surface Bodies (panels) and/or Line Bodies (beams)?
- Does the diffraction analysis succeed if you turn off the 'Generate Wave Grid Pressures' option in the Hydrodynamic Diffraction Analysis Settings?