A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
I remember Excel 2003 had a limit of 30 arguments for the MIN function, I think it went up to the current 255 arguments in Excel 2007.
This is a guess: try using 2 MIN functions (3 actually):
=IF(D6="",0,MIN(MIN(D9,D13,D17,D21,D26,D30,D34,D38,D43,D47,D51,D55,D59,D64,D68,D72,D76,D81,D85,D89,D93,D98,D102,D106,D110),MIN(D115,D119,D123,D127,D132,D136,D140,D144,D149,D153,D157,D161)))
Edit: If you're using .xlsx files that implies that you're using at least Excel 2007, so I'm guessing you're in Compatibility mode (you'll see it at the top of the Excel window) having opened a .xls file. So try saving the file as an xlsx file whereupon your original formula should work.