The red exclamation point on your MS-Excel file icon indicates that there is an issue with the file. It means that Excel is unable to locate or access the file's external references, such as links to other workbooks or data sources. This can happen if the file has been moved or if the external references have been deleted or renamed.

To resolve this issue, you can try the following steps:

1. Open the file in Excel and check for any error messages or warnings that may indicate the source of the problem.
   
2. Check the file's external references by going to the "Edit" menu and selecting "Links". This will show you a list of all the external references in the file. If any of them are broken or missing, you can update them by clicking on the "Change Source" button.
   
3. If the file has been moved, you can try moving it back to its original location or updating the external references to point to the new location.
   
4. If the file contains links to other workbooks or data sources, make sure that those files are still available and accessible.

Once you have resolved the issue, save the file and the red exclamation point should disappear from the icon.