Hi,
What version of Excel are you using? What is the file extension when you
try to open it - .XLS? Also, are you opening the file from inside Excel, or
from an email attachment, or by double-clicking in the Explorer window. Try
each and see if it makes a difference.
Sometimes this helps -
Tools, Options, General, uncheck Ignore other applications
In Excel 2007, go to the office button, choose excel options, under the
"advanced" tab, click "ignore other apps that use DDE".