The problem is that when the JET engine pulls in the Excel spreadsheet it will (by default) read just the first 8 rows to determine what the column datatype should be. If the row that has the +255 entry is after row 8 JET will pick the DT-WSTR (255) datatype. You have two methods of solving your problem.

1. either move the row with the +255 data column to become one of the 1st 8 rows.

2. go to the following link and read how to change your Excel registry to read more than 8 rows. http://support.microsoft.com/kb/281517