OLE DB provider cannot connect to Excel 2007 with 400 columns

[kei]

I use a Delphi 7 TADOConnection (e.g. connection1) to connect a Excel 2007
file with about 400 columns in a worksheet, using the following
connectionString:
Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\temp\exportFG.xlsx;Extended
Properties="Excel 12.0;HDR=YES;"
when I set the connected properties to true, no error occur.
but when i put a TADOTable and set its connection to connection1,
tableDirect = true, only 256 columns can be retrieved!! is this a limitation
of the OLE DB provider for Excel? (I know before Excel 2007, a worksheet has
maximum
256 columns only)