A Jacobian determinant is a measure used within LUSAS to give an accurate value of the current length, area or volume of an element. A magnitude of less than or equal to zero will automatically invoke this message and may be a result of...

1. Incorrect definition of the two/three dimensional continuum, shell and plate elements
   This can occur if there is a probelm with the geometry that is being meshed, that leads to invalid definition of elements when meshed.  For example, a surface with self-intersecting sides or a volume with self-intersecting faces.  The offending surface or volume in such case should be redefined and then remeshed.
2. A load increment that is too large and causing massive deformation of one or more elements, e.g., the elements are inverting. Note that this would only occur in geometrically nonlinear analyses.
3. When using the nonlinear rubber material it is possible to obtain this error if too low a magnitude of the bulk modulus is specified and/or the incremental load level is too high. In both cases the incompressibility of the material may be insufficient to resist the applied load level and, because geometric nonlinearity is typically required with such materials, the elements can be inverted.