From http://microsoftdw.blogspot.com/, good blog for SSIS
So sometimes you have data that does not come up right in Excel because either it's not formatted, or it's got mixed types. The end of it all is you just need it to come in as text and you can convert it later. My good friend, Robert Skoglund gave me this hint and I dug up some info on it....
Basically, add the option IMEX=1 to the ConnectionString for Excel. This forces the columns to be treated all as text.
This from ConnectionStrings.com....
From Microsoft.....
http://msdn2.microsoft.com/en-us/library/ms254500.aspx
Credit, where credit is due....
http://www.dicks-blog.com/archives/2004/06/03/external-data-mixed-data-types/