You have exceeded the maximum number of daily map requests allowed by Google.
See the usage limits and terms of service here:
Ugh! Correct answer, thank you jml. What might some helpful solutions be?
That depends on your intended use for the map and which limit you are exceeding.
If you are exceeding the limit of 50 static map requests per minute from the same IP address, perhaps you can simplify the map by reducing the number of markers or paths on the map request.
If it is not happening too often, ask your customers to wait for the quota to be reset after 24 hours before using the map reference again.
Otherwise, you may have to apply for an API key from Google: