This question is probably better addressed to the [Ushahidi help forums][1], but a quick search on their site suggests you need an API key if you are using Google Maps as your base layer - see pages 8 (9/95) and 12 (13/95) in the [user manual][2].
Note in particular the paragraph:
"Because of the way Ushahidi is configured as well, even if you choose Yahoo or OSM,
you’ll need to enter a Google API key. Click the link beside that field to get one for your
domain and enter in the value provided."
[1]: http://forums.ushahidi.com/search.php?q=api+key
[2]: http://wiki.ushahidi.com/download/attachments/622608/Ushahidi-Manual.pdf?version=1&modificationDate=1331131656530