I came across this error when I was attempting to import data from an Excel spreadsheet into a SQL database using SQL Server Integration Services (SSIS) 2005.  The error occurs because by default the Excel driver only reads the first eight rows of the spreadsheet when it determines the column data type and data length.

If you have a spreadsheet where the first eight rows aren’t representative of the data in the spreadsheet, you can increase the number of rows that are sampled by editing the TypeGuessRows value under the following registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Jet\4.0\Engines\Excel

See here for more details http://technet.microsoft.com/en-us/library/ms141683(v=sql.90).aspx.