Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.

One of strange error that i had to deal with is the one mentioned above. The error used to prompt more frequently when the number of records increased in table. So at the initial stage of developments you won't have this timeout error. But when the system is in operation level and when the production data increases you may haev to come across this timeout error.

There are two main Timeout property in ADO.NET.

1. Connection Timeout for Connection
2. Timeout for Data Access( Command Object or DataAdapter)

Setting Connection Timeout property for SQLConnnection object ?

You can't set timeout property in connection object because its a READ ONLY property.

The proper way to do this is to set the timeout value in connection string as mentioned below.

SqlConnection conn = new SqlConnection("server=Server;uid=sa;pwd=123456;database=myDB;Connection Timeout=120");

Setting the timeout property in DataAdapter or CommandObject.

SqlDataAdapter sqlAdapter = new SqlDataAdapter();
sqlAdapter.SelectCommand = new SqlCommand(sqlQuery, conn);
sqlAdapter.SelectCommand.CommandTimeout = 0;

Setting the timeout value to 0 will makes adapter or command to wait for indefinite time before terminating the attempt to execute a command and generating an error. The default timeout value for connection object is 15 seconds.

hope this might help you to solve the problem.