There are many occasions when you try to open an .xls file from the forum and you get an error.
Such as this thread.
.
Name:  pic1.jpg
Views: 57
Size:  66.9 KB

Error!
Open the file location to see where the file is and it looks fine.
'
Name:  pic3.jpg
Views: 35
Size:  92.0 KB

In file explorer, select the "View" tab then check "File name extensions".
You will see ".xlsx" has been added to the end.
.
Name:  pic6.jpg
Views: 33
Size:  139.1 KB

Remove the ".xlsx" extension. Select "Yes" to confirm you want to remove it.

Open the file.

.
Name:  pic8.jpg
Views: 35
Size:  43.0 KB
.
Name:  pic9.jpg
Views: 34
Size:  138.9 KB