If you get a big red X (cross) in Google Earth, this is because the overlayed image referenced in a loaded KML file has disappeared or is inaccessible.
To remove the big red X in Google Earth, untick the Placemarks in the Places panel until you find the offending placemark causing the big red X. You can then right click the placemark and click Delete Contents to fix this.
Alternatively you can right click on the top level folder and Delete Contents on them all if there are no important places that need saved. This will fix up Google Earth to a default state to remove the big red X, after doing this you should then try to create your kml file again in Quickmap.