Every so often I experience problems importing data from Office files (usually XLS) into SQL. Sometimes everything works fine, others not. I've always suspected it's because I don't actually have Office installed on my Windows part of my Mac, although I do have SQL, SQL Express, and an old copy of Access.
This morning I was importing an XLS with a couple of thousand lines, into SQL 2008. And up popped this message:
The microsoft.ace.oledb.12.0 provider is not registered on the local machine
A quick Google and I found this forum which leads to this Microsoft download page for the 2007 Office System Driver: Data Connectivity Components. I downloaded and installed and now SQL likes my XLS file.
David Eedle 
Installing the Office Connectivity drivers 2010 solved my problem. I had to restart the server though.
http://www.microsoft.com/download/en/details.aspx?id=13255