There are a few times you can see that message.
A. Change original file name in any way. you would need to UPDATE the link
B. As Pert said some browsers extensions. Try opening it in INCOGNITO or similar window.
C. The file may have had a NON ALLOWED type of extra tab. Remove the offending tab.
D. You included large image files on the extra tabs. Delete images from sketch and resize before adding back.
E. You did not have AUTOSAVE turned on or forgot to save it. Turn on AUTOSAVE in preferences.
There may be a couple more things but I cannot remember them all right now.