All nodes in the analysis must be associated with valid elements. Disconnected nodes in the model are generally ignored, but this error indicates that a node which is not connected to valid elements has somehow been included in the analysis mesh.
Locate the node specified in the message using Modeling Query Entities, and check that the mesh in that region is valid. Remesh the geometry starting from a better quality Dual Domain mesh (less high aspect ratio triangles). If the problem persists, contact Technical Support.