This message appears when the Solver could not allocate the memory it needs to solve the problem.  However, since Microsoft Windows supports a “virtual memory” much larger than your available RAM by swapping data to your hard disk, before you see this message you are likely to notice that solution times have greatly slowed down, and the hard disk activity light in your PC is flickering during the solution process, or even when “Analyzing Solver Model,” “Diagnosing Problem Function” or “Setting Up Problem” appears on the Excel status bar.

The Polymorphic Spreadsheet Interpreter in Analytic Solver can use a considerable amount of memory, when you solve a problem by clicking the Optimize icon on the Ribbon or the Solve icon on the Solver Task Pane, and when you click Optimize – Analyze Original Model on the Ribbon.  You can progressively reduce the memory used by the Interpreter by taking the following actions in order, using the Solver Model dialog:

Check the Sparse box in the Advanced options group.

Set the Check For option to Gradients.

Set the Solve With option to Excel Interpreter.

When Solve With = Excel Interpreter, the PSI Interpreter is not used and does not use any memory; any further problems are due to memory demands of the Solver engines, Microsoft Excel and Windows.  You can save some memory by closing any Windows applications other than Excel, closing programs that run in the System Tray, and closing any Excel workbooks not needed to solve the problem.