When running a model I get the following error message:

stdout | warning | <p>Solving linear system 233 fails at time 8.66021e-010. For more information use -lv LOG_LS.</p>
LOG_LS | warning | <p>Failed to solve linear system of equations (no. 233) at time 0.000000, system is singular for U[2, 2].</p>
LOG_LS | warning | <p>The default linear solver fails, the fallback solver with total pivoting is started at time 0.000000. That might raise performance issues, for more information use -lv LOG_LS.</p>
LOG_LS | warning | <p>Matrix singular!</p>
LOG_LS | warning | <p>under-determined linear system not solvable!</p>
stdout | warning | <p>Error solving linear system of equations (no. 233) at time 0.000000.</p>
stdout | warning | <p>Solving linear system 233 fails at time 8.66021e-010. For more information use -lv LOG_LS.</p>


When debugging I see that equation # 233 is the following one:

Index     Type       Equation
233      regular     linear, size=46

The other equations are model equations, that can be understood, but this one, I suppose, has a special meaning that I don't know.

Any suggestions?