Before you upload source files to Maps Engine, ensure that each file conforms to the specifications listed in Supported data formats and limits. Each main file must be accompanied by all required associated files. As an example, if you are uploading a shapefile (.shp), you'll need to select its associated .shx and .dbf file; look for other files that have the same filename as the main file, but with different extensions. It's critical that data is formatted properly before upload.