If you are using Symantec/Norton AntiVirus, try disabling the
Office Plugin that comes with it (but don't disable Norton
AutoProtect). See http://support.microsoft.com/?kbid=329820 "How
to use Office programs with the Norton AntiVirus Office plug-in"
for more information.

Blue Max wrote:

In Excel 2007 (Beta Technical Refresh) we're unable to open our existing
worksheets. When we open a worksheet we get the error message that our
antivirus software is preventing our worksheet from loading because it is
infected. The files are fine, they are not infected, but they do have
embedded macros. We used to simply get a dialog that allowed us to confirm
that we wanted to open the worksheet with macros enabled, but now we can't
open the worksheets at all.