I’m going to guess you are on WordPress 3.9 ?
This is a bug with the new version of WordPress and last I remember, this was brought to their attention to their development team. In the mean time, try this temporary fix which I found on another site and see if it works…
Open the theme file called “custom-header.php” which is found here:
/wp-content / themes / celestial / includes / custom-header.php