Unfortunately there is no way to see which edges CST is referring to and that is not that important as well as all we need is to solve the issue. Sometimes this message just comes as warning and can be and should be ignored unless you are very much concerned about the accuracy of the simulation. There is no one rule to define the proper mesh and things change from the type of problem to the type of geometry in question and type of solver being used. Try to change the mesh type means switching between the tetrahedral and hexahedral types of mesh and use the local mesh refinements and generate and evaluate the mesh before running the simulation. Usually this error occurs when mesh is very crude.