Uncaught TypeError: Cannot read property 'firstChild' of null

I have a problem with Visitor Map page.
It works fine in the block, but when I click on the menu link /visitorinfo-map, the map isn't displayed and the map in the block disappears as well.

In Google Chrome I see an error:

main,js:458 Uncaught TypeError: Cannot read property 'firstChild' of null

http://maps.gstatic.com/intl/en_ALL/mapfiles/310c/maps2.api/main.js

458: function pg(a){for(var b;b=a.firstChild;){uh(b);a.removeChild(b)}}

~~~~~~~~~~~~~~~~~

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