Using External Data from an Excel File

[Erl072408]

We are using a very simple excel file as external data.  The file has 6 columns.  Data is contained in all 6 columns, but not necessarity every row has all 6 columns filled.  If the first row contains blank data in one of the columns that column does not import.  However when we made sure that the first row of data contained data in every column the column would import.  Any ideas?  Is there a setting that needs to be changed?