Open Chrome, and press f12 and click on the console tab. Look for the following errors:
“MAXIMUM CALL STACK EXCEEDED” – This is most likely an issue with the lat/lng entered on the editor defaults in the settings page. It can also be down to a lat/lng entered for a location. Map List Pro uses the decimal lat/lng system so locations should look like this: 51.62921, -0.7545. There should be no degree signs etc.
“Unable to set offsetwidth of undefined” – If the shortcode is called more than once (sometimes this happens if a theme or plugin runs through the content more than once). This should only be an issue with early versions of Map List Pro so try upgrading.
“Uncaught TypeError: Object #<Object> has no method ‘on’“ – This error normally meant that an old version of jquery (1.4.2 or lower) is being used. Map List Pro requires jQuery 1.7 or higher. It may be worth checking to see if your theme has an update, or if you can update jQuery directly.