A network-related or instance-specific error

Question

Hi all,

 

I got an error like this when i'm gonna run asp.net web forms

 

why is that? How should i prevent this error.

 

Server Error in '/' Application.

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Data.SqlClient.SqlException: A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

Source Error:

Line 85:

Line 86:

Line 87: con.Open();

Line 88: string pcount = Convert.ToString(command.ExecuteScalar());

Line 89: if (pcount.Length == 0)