Excel 2007 - ADO - More than 65536 rows - Problem ?
 

Check the data for:

1. Single quotes
2. Linefeeds
3. Unusually long strings

To be on the safe side, copy the first 50K rows into the WorkSheet a
bunch of times to confirm that the problem *really* has to do with the
number of rows.

If all else fails - move the data out of Excel and into a database.
Organize the data like a normal person.