I got the same error whilst using Excel 2003 DLLs and trying to write to the 257th column. Excel 2003 limits maximum column per worksheet to 256, thus raising this exception.
For detailed limitations of Excel 2003, see http://office.microsoft.com/en-001/excel-help/excel-specifications-and-limits-HP005199291.aspx
Starting from Excel 2007, column limitation is increased to 16384 columns, see http://office.microsoft.com/en-001/excel-help/excel-specifications-and-limits-HP010073849.aspx