The timeout period elapsed prior to obtaining a connection from the pool.

Error:"Timeout expired.  The timeout period elapsed prior to obtaining a connection from the pool.  This may have occurred because all pooled connections were in use and max pool size was reached." 

Discription:

When you open an SQL Connection object, it always takes from an available pool of connections. When you close the connection, asp.net will release the connection to the pool of connections so that next connection object can use it.

If you open connections with out closing them and when the pool reaches maximum connections, it will throw the specified error. Make sure you are not opening connection inside loop, if you open connection make sure you are closing it immedietly after you execute the query.

Solution:
You can try the following things

1. Always close your connection in the finally block

2. Increase pool size like in your connection string
3. Don't use pooling at all