Error in LDLt decomposition

Hello comunity,
I have started a simulation with a simple geometry defined by an ellipsoid and inside it a cube with a square in on of its faces corresponding to the thruster. The mesh is defined as following:
Mesh size at the ellipsoide: 10;
Mesh size at the surface of the cube: 2;
Mesh size at the thruster:1;
When the simulation starts, an error pop up defined as following:
error in LDLt decomposition in assembPrecontNonLinear=7.
Does anybody know what can be the source of this error?
Thank you very much,

Hello Yago,
did you check the mesh quality