You might want to check out AcSpreadSheetTypes
You have
Code:
DoCmd.TransferSpreadsheet acExport, acSpreadsheetTypeExcel12, "Unfiltered Master Query", , -1
Disregarding the missing Path/FileName issue, you should be using acSpreadsheetTypeExcel12Xml for Office 2010 and higher, and use the extension of ".xlsx".
My Excel2010 can handle 1,048,576 rows.
The TransferSpreadsheet command should look something like:
Code:
DoCmd.TransferSpreadsheet acExport, acSpreadsheetTypeExcel12Xml, "UnfilteredMasterQuery", "F:\MyMasterExport.xlsx", True
If you use "acSpreadsheetTypeExcel12" and the filename extension is ".xls", you could/would be running in compatibility mode, which would limit you to the old standard of 65k.
Note that "acSpreadsheetTypeExcel12" is for Excel 2007
PS: you cam save yourself lots of grief if you DO NOT use spaces in Access object names.
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Bad: "Unfiltered Master Query"
Better: "Unfiltered_Master_Query"
Best: "UnfilteredMasterQuery"