"David" wrote.

The problem comes when the C# program calls the Excel
macro that calls the Solver function, I get the
infamous "Solver: An unexpected internal error occurred,
or available memory was exhausted." error message.

David,

would you be interested to test this with ManagedXLL
(http://ManagedXLL.net/)? Contact me and I'll provide you with an
evaluation.

Best regards,

Jens Thiel

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