I have a file that has an original file format .xls

I saved as .xlsx (I am using Excel 2007) with a different name so I could make changes to the new file without changing the original.

That helped turn off compatibilty mode.... but it is still "shared". While it is shared I cannot delete a sheet. In fact, I really don't even want it to be shared. If the file is open, and someone else opens it, I want it to open as "read only". I cannot uncheck the "Allow changes by more than one user at the same time. This also allows workbook merging." checkbox because it is greyed out.


Any Suggestions?