9. Solver encountered an error value in a target or constraint cell.

This message appears when the Solver recalculates your worksheet using a new set of values for the decision variables (adjustable or changing cells), and discovers an error value (such as ERR or NA) in the cell calculating the objective (Target Cell) or one of the constraints. Inspecting the worksheet for error values like these will usually indicate the source of the problem. If you have entered formulas for the right hand sides of certain constraints, the error might have occurred in one of these formulas rather than in a cell on the worksheet. For this and other reasons, we recommend that you use only constants and cell references on the right hand sides of constraints. If you use a formula, be sure to include explicit sheet letters on any cell references, such as 1+A:C1.

Look for names or cell references to rows or columns that you have deleted, or for unanticipated values of the decision variables which lead to arguments outside the domains of your functions -- such as a negative value supplied to @SQRT. You can often add constraints to avoid such domain errors; if you have trouble with a constraint such as A1 >= 0, try a constraint such as A1 >= 0.00001 instead.