Excel 2003 you had a limit of 65535 rows, check the version of the interop libraries you are using.
The name of the library for 2003 is “Microsoft Excel 12.0 Object Library”, the name for 2010 is “Microsoft Excel 15.0 Object Library”.
If you change your references to 15+ you should be able to use up to a million ish rows.
Interop libraries use the COM (Component Object Model) interface, the Excel application will need to be installed on the dev machine and the machine the application will be running on. You can’t distribute the interops as part of your application, they need to be available on the machines GAC
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