If you are handling large databases and big application(s) that are running on servers in a cluster, then probably this error might have occurred. In an ASP.NET app, we can use connection pooling that helps to share the connection between multiple request(s) rather than creating more connections. The settings relating to connection pool are defined in web.config file. Max pool size reached error in ASP.NET occurs, when the number of connections go beyond the maximum defined limit in Web.config file. Following are the various settings of the Connection Pooling: Name Default Description Connection Lifetime 0 When a connection is returned to the pool, its creation time is compared with the current time, and the connection is destroyed if that time span (in seconds) exceeds the value specified by Connection Lifetime . This is useful in clustered configurations to force load balancing between a running se