Here are some possible issues to look for and solutions to them to help you save changes to your Excel data:

1. Check that the file extension is an allowed file type for saving in Excel.
2. Verify that there is enough available space on your device to save the Excel file.
3. Try saving a copy of the file to a different place, for a change, such as your desktop or a USB drive.
4. Disable any Anti-Virus programs temporarily that may be preventing you from saving the file.
5. Re-start your computer and try saving the file again.