You can clear the pool use the following code. However i suggest you to check the following first
1. Please call the Dispose() method after you close the connection.
2. Ask the DBA to check for open connections at the very moment you are greeted with the error. You could find the faulty application.
3. Check the web.config for the pool settings. Set pooling to true.
Max Pool Size - Leave it at 100
Min Pool Size - Mark it 0
Pooling - Mark to true
4. Note: Restarting the IIS could fix the issue. Because the AppPools would refresh. If all does not work, then do this.
//To clear the specific connection
//To clear all pools