It sounds like Google may have throttled your IP for excessive queries. If so, you'll have to wait a bit before you continue — sometimes 10-15 minutes, other times the next day if egregious.
The ideal solution is to use Proxies so that your queries will be distributed across as many proxies as you use.
Regardless if you use proxies or not, make sure to set a reasonable pause interval between requests when you're running batch queries against Google. You can do this using HttpSettings() — I recommend a random delay between 500 and 3000 If Same Host as shown below: