To troubleshoot the issue I'd strip the search down to the minimum amount of fields required for it to work; latitude and longitude.
index=myindex latitude=\* longitude=\* | table latitude, longitude
If the graph fails to render with latitude and longitude you most likely have some bad values (not integers or floating point numbers) in either or both of the fields. You can use the following search to identify which events have latitude or longitude fields that aren't floating point numbers.
index=myindex latitude=\* longitude=\* | eval not_latitude=if(match(latitude, "[-+]?[0-9]\*\.?[0-9]+"), 0, 1), not_longitude=if(match(longitude, "[-+]?[0-9]\*\.?[0-9]+"), 0, 1) | search not_latitude=1 OR not_longitude=1
If you have bad latitude or longitude fields then you'll need to clean it up with an eval or exclude it somehow. The error messages for custom visualizations are very generic and there isn't an easy way to validate user input so I know how frustrating it can be to troubleshoot. Let me know if that doesn't solve your issue.
