Cannot save workspace
 

I tried saving a workspace in Excel using the Save Workspace box in the View
tab. I created my file name and hit save. A message box pops up telling me I
cannot save in this file extension and I have to change the file extension.
How do I do this? I opened 4 worksheets that I was trying to create the
workspace from? Any help would be appreciated. Thank you BTW: I am using
Office 2007.