Answer:
The message means that your structural system is numerically unstable. Such instability is often caused by incorrect support conditions or hinge definitions in RF‑/FE‑LTB. Therefore, check the degrees of freedom of the continuous member in Window 1.4 Nodal Supports and Window 1.7 Member Hinges.
The reason: When selecting the imperfections, and also in the calculation, the critical load factor is specified. Based on this, the critical load factor of the structure is determined. This is characterized by the fact that either the determinant of the stiffness matrix becomes zero, or very high deformations occur for very small load increments in the calculation.
