If you are using the Evolutionary Solver, this message appears when (i) the Solver has found the maximum number of feasible solutions (values for the variables that satisfy all constraints) allowed by the Max Feasible Sols options setting on the Engine tab of the Solver Task Pane and (ii) you clicked on the Stop button when the Solver displayed the Show Trial Solution dialog. You may increase the value in the Max Feasible Sols box, or click on the Continue button instead of the Stop button in the Show Trial Solution dialog to continue the solution process.
If you are using one of the other Solver engines on a problem with integer constraints, this message appears when (i) the Solver has found the maximum number of integer solutions (values for the variables that satisfy all constraints, including the integer constraints) allowed by the Max Integer Sols option setting on the Engine tab of the Solver Task Pane and (ii) you clicked on the Stop button when the Solver displayed the Show Trial Solution dialog. You may increase the value for the Max Integer Sols option, or click on the Continue button instead of the Stop button in the Show Trial Solution dialog. But you should also consider whether the problem is formulated correctly, and whether you can add constraints to “tighten” the formulation. If you are using the LP/Quadratic Solver in Analytic Solver Comprehensive or Analytic Solver Optimization, try activating more Cuts and Heuristics in the Integer section of the Task Pane Engine tab.