Excel 2007 file format error

After I have upgraded my MSOffice from 2003 to 2007, I have problem opening a excel file in the form of .xlw

Error says "The filename.xlw is in a different format than specified by the file extension, verify that the file is not corrupted and is from a trusted source."

Once I click on the Yes button, a box pop out that says "Name Conflict, Name cannot be the same as a built in name.
old name: Print_Area
New name: "

I am stuck here.

anyone please advise,