Symptom: Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding.
- SqlConnection: If this happen when tries to connecting to SQL Server, then try increasing the timeout of the connection Connection String: server=Server;database=Database;uid=Uid;pwd=Pwd;timeout=600 (ConnectionTimeout is read-only)
- SqlCommand: More interestingly if you manage to connect successfully and although you set a fat timeout value to your connection command object does not inherit the timeout from its connection. It uses its own timeout value. More logically ConnectionTimeout and CommandTimeout.
command.CommandTimeot = 600 (set to 10 minutes)
Reference: ASP.NET Forums