Tool requires a valid executable. If you do not want to save this tool, click Delete in the External Tools dialog.
This error generally occurs when a tool has been added to the External Tools dialog box, but no executable has been specified.
To correct this error
If you intend to save the tool, click OK and enter a file name in the Command box for the tool or browse to a file by choosing the ellipsis button.
If you do not intent to save the tool, click OK and then click Delete in the External Tools dialog box.