The problem is the the connection in the pool is over.Means you are trying to get connection from the Pool and the pool doesnt have any more connection available.For this, you should increase the no. of connections in the connection pool by setting the properties in config.xml/or form the console.
Please note that if such problems comes regularly then there is some leakage of connections which means that you are not closing the Connections after using it.
Thanks
Harsh