Check your SourceExcelConnection Properties.

For the Connection String, make sure "IMEX=1;" is present Under the variable of Extended Properties. For example:

Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Documents and Settings\user\Desktop\Data\January 2009\MyExcelData.xls;Extended Properties="EXCEL 8.0;HDR=YES;IMEX=1";

Normally the IMEX part will...