Check the three points listed below:
1. Make sure your database engine is configured to accept remote connections(I you are using centralized database)
Quote:
•Start -> All Programs -> SQL Server 2005 -> Configuration Tools -> SQL Server Surface Area Configuration
•Click on Surface Area Configuration for Services and Connections
•Select the instance that is having a problem -> Database Engine -> Remote Connections
•Enable local and remote connections
•Restart instance
2. Check the SQL Server service account
Quote:
•If you are not using a domain account as a service account (for example if you are using NETWORK SERVICE), you may want to switch this first before proceeding
3.If you are using a named SQL Server instance, make sure you are using that instance name in your connection strings in your ASweb P.NET application
Quote:
•Usually the format needed to specify the database server is machinename\instancename
•Check your connection string as well.
Refer the link below:
A network-related or instance-specific error occurred while establishing a connection to SQL Server[
^]
--Amit