Ok, I'm sure there's an easy way around this...

As part of the course, students need to show how to password protect an Excel workbook, but when you enable the protect workbook option, and then try to save, you get a message which says: "The document saved successfully, but Excel cannot re-open it because of a sharing violation. Please close the document and try to open it again."

When you try to open the workbook, it says: "Excel cannot open the file 'test.xlsx' because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file."

I assume there's a way around this in Management Console with permissions?

Thanks in advance...