**By Changing Cells must be on the active sheet.**

A limitation of the Solver is that all of the decision variables (adjustable or changing cells) in the By Changing Cells edit box must be cells on the active sheet. (This limitation makes the Solver considerably faster than if adjustable cells were allowed to be on any sheet.) You should re-design your Solver model so that all decision variables are on one sheet, and try again.

**Cannot Guess By Changing Cells without a Set Cell.**

You clicked on the Guess button without first specifying a cell in the Set Cell edit box. When you click on this button, the Solver determines all "leaf" (non-formula) cells on which the Set cell depends, and places a reference to these cells in the By Changing Cells edit box. This reference will always include the actual decision variables as a subset.

**Cell Reference box is empty or contents is not valid.**

In the Add/Change Constraint dialog, you clicked OK while the Cell Reference edit box is empty or contains something other than a valid cell reference (which may be a range of cells or a defined name). Correct the contents of the Cell Reference edit box and try again.

**Constraint must be a number, simple reference, or formula with a numeric value.**

In the Add/Change Constraint dialog, you clicked OK while the Constraint edit box is empty or doesn't contain one of the valid forms for a constraint right hand side: A number, simple cell reference (including a defined name), or a formula with a numeric value. Correct the contents of the Constraint edit box and try again.

**Integer constraint Cell Reference must include only By Changing Cells.**

In the Add/Change Constraint dialog, you chose "int" from the constraint relation dropdown list, but the cells referenced in the Cell Reference edit box are not all decision variables (adjustable or changing cells). In the Solver, only decision variables may be constrained to have integer values. For more information on this topic, consult How the Solver handles Constraints [TBD].

**Reset all Solver options and cell selections?**

This is a confirmation message which appears when you click on the Reset All button. When you OK this message, all of the adjustable cell, target cell, and constraint information currently in the Solver Parameters dialog, and any non-default selections in the Solver options dialog will be erased.

**Set Cell contents must be a formula.
Set Cell must be a single cell on the active sheet.
Set Cell must have precedents containing numbers on the active sheet.**

One of these messages appears when you click on a button if the Set Cell edit box contains something which cannot serve as the objective function in a Solver problem. The Set Cell must refer to a single calculated value, on the active sheet, which is to be maximized, minimized or made equal to the target value. In order for the Solver to change the value of the Set Cell, it must contain a formula which depends on cells on the active sheet, some of which must be adjustable cells (in the By Changing Cells edit box). If you receive one of these messages, check and modify your Set Cell selection and try again.

**Too many adjustable cells.**

This message appears when you click on a button in the Solver Parameters dialog if the number of cells referenced in the By Changing Cells edit box exceeds the Solver's limit (200 in the case of the standard Microsoft Excel Solver). For help with this message, consult Standard Excel Solver: Dealing with Problem Size Limits. Frontline's Premium Solver products can handle problems with much larger numbers of adjustable cells.

**Too many constraints.**

This message appears when you click OK (or Add) in the Add/Change Constraint dialog if the number of cells in the Cell Reference edit box exceeds the Solver's limit. If the total number of cells referenced in all constraints in the Constraint list box exceeds the Solver's limit, you will receive another message, "The problem is too large for Solver to handle," when you click Solve. For more information on the limits, consult Standard Excel Solver: Dealing with Problem Size Limits. Frontline's Premium Solver products can handle problems with much larger numbers of constraints.

**Unequal number of cells in Cell Reference and Constraint.**

This message appears when you click OK (or Add) in the Add/Change Constraint dialog if you have entered a multi-cell reference in the Constraint edit box, and the number of cells referenced on the left hand side (Cell Reference edit box) is not equal to the number of cells referenced on the right hand side (Constraint edit box). Modify the appropriate edit box and try again.

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