TypeGuessRows

If problem with data format when loading an Excel file to Excel, it might help to change the value of TypeGuessRows in the registry: 

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Jet\4.0\Engines\Excel

The value of this key is how many rows in the Excel file that is read to determine what data type each column has.

If you set it to 0 (zero) all rows is read.

The default value is 8 or 25 (hex 19), not sure which.