in the lst file, you can find which equation conopt finds problematic during presolve.

```
**** ERRORS/WARNINGS IN EQUATION Eq_klav
1 error(s): Inconsistency in pre-triangular part of model.
```

Looking at your code I see equation EQ_klav uses variable totlav which is defined through equation Eq_totlav.

```
Eq_totlav ('sallab',m).. totlav('sallab') =e= aqlav ('sallab',m);
Eq_klav.. klav =e= sum (ltype, totlav(ltype)*lab_wage(ltype));
```

I do not understand the model in depth but equation Eq_totlav looks wrong to me. You are generating 12 constraints through this equation that basically would cause aqlav(sallab,) being identical for all month:

```
---- Eq_totlav =E= labour requirements for each cluster and each farmtype
Eq_totlav(sallab,GEN).. - aqlav(sallab,GEN) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,FEB).. - aqlav(sallab,FEB) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,MAR).. - aqlav(sallab,MAR) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,APR).. - aqlav(sallab,APR) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,MAG).. - aqlav(sallab,MAG) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,GIU).. - aqlav(sallab,GIU) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,LUG).. - aqlav(sallab,LUG) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,AGO).. - aqlav(sallab,AGO) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,SET).. - aqlav(sallab,SET) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,OTT).. - aqlav(sallab,OTT) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,NOV).. - aqlav(sallab,NOV) + totlav(sallab) =E= 0 ; (LHS = 0)
Eq_totlav(sallab,DIC).. - aqlav(sallab,DIC) + totlav(sallab) =E= 0 ; (LHS = 0)
```

I guess what you want might be something like this:

```
Eq_totlav ('sallab').. totlav('sallab') =e= sum(m, aqlav ('sallab',m));
```

where totlav is the sum of aqlav over all months:

```
---- Eq_totlav =E= labour requirements for each cluster and each farmtype
Eq_totlav(sallab).. - aqlav(sallab,GEN) - aqlav(sallab,FEB) - aqlav(sallab,MAR) - aqlav(sallab,APR) - aqlav(sallab,MAG) - aqlav(sallab,GIU) - aqlav(sallab,LUG) - aqlav(sallab,AGO) - aqlav(sallab,SET) - aqlav(sallab,OTT) - aqlav(sallab,NOV) - aqlav(sallab,DIC) + totlav(sallab) =E= 0 ; (LHS = 0)
```

This is just a guess… I hope this helps!

Fred