81. NO FEASIBLE SOLUTION FOUND.

LINGO was unable to find a solution that simultaneously satisfies all the constraints.  Here are some suggestions:

Check the model’s consistency.
Run the Solver|Debug command to have LINGO search for minimal infeasible constraint sets.  Note: LINGO may not be able to complete this command in a reasonable amount of time on large and/or difficult models.
Try dropping constraints until the problem goes away to get an idea of where the trouble may lie.
Check the solution report. Constraints contributing to the infeasibility will have a nonzero dual price.