Are you working from a VM? Because the error 26 is regarding remote connections not being allowed.
Try this:
- Go to Start
- All Programs
- SQL Server 2005
- Configuration tools
- Surface Area Configuration
- Now hit on Surface Configuration for Services and connections
- Then hit on Remote Connections
- There you need to select the type of connection you are going to be using
- Apply changes
- Then go to Services
- Restart you Database Engine
- Then start the SQL Browser as well
- Then configure the Firewall by adding C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Binn\sqlservr.exe and C:\Program Files\Microsoft SQL Server\90\Shared\sqlbrowser.exe(or wherever you have this installed) as exeptions
You can check on further information here:
And just in case here are the screenshots of the process (sorry that these are in spanish but that is the language I have my SQL Server running on)