Google Geocoding Api “OVER_QUERY_LIMIT”

Question

i am using Google geocoding api with its api Key,i am using code as below:

 

 string url = "https://maps.googleapis.com/maps/api/geocode/xml?address=" + area + "," + City + "&Key=ABZIXXXXXXXXXXXXXXXXXXXXXXXXXXX"

 

 

After handling some request i am getting status code "OVER_QUERY_LIMIT", does any one have any idea about this problem?