The error is very generic. It may be due to bad geometry. Please check geometry in SpaceClaim. Select geometry in structure tree --> Use right click --> Select Check Geometry. (Or Tools - Fault Detection in DM) The geometry should be error free to proceed. If geometry has any errors, please modify/recreate geometry at those places.
The error may be due to intersecting bodies as well. Pelase check Interference tool in Fluent Meshing.
The error may be due to wrong sizing in Fluent Meshing. Please make sure that you provide correct sizing at various places.