SQL Server does not exist or access denied.

Cause:
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Not enabled protocols on SQLExpress box as well as client box
Firewall blocking issue of port and service

Resolution:
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1. Checked the protocols whether its enabled
2. Ran the command cliconfg from start---Run on local box and enabled both tcp/ip and named pipes
3. Done the same on the SQLExpress box
4. went to SQLServer 2005 Surface area configuration and changed the services and connections set the local and remote connections to use both tcp/ip and named pipes
5. Typed in start---run----firewall.cpl
6. Went to exceptions tab and added the following services to it
C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Binn\sqlservr.exe executable program
C:\Program Files\Microsoft SQL Server\90\Shared\sqlbrowser.exe executable program
7. Add the port of SQLExpress 1433 to exception list
8. Restarted the service
9. browsed the application and it was working fine without any errors.