An error has occurred while establishing a connection to the server. When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server
Does this error look familiar. Well, when working with the "Aspnet_regsql.exe"(a.k.a. Asp.net sql server registration tool) Tool, you can configure your existing database to store tables, stored procedures, and functions related to the Built-in Membership, Profile, Role Management, and Personalization Providers that ships with Asp.net 2.0. When attempting this process you will sometimes encounter the error above or more like the one below:

To resolve this issue, simple change the server name to the instance name for the database. (Ex. "Myserver\sqlexpress" instead of "Myserver") You should now be able to click the "Database" drop down error without recieving an error message. Make note of the screen shot below:

I hope this helps. Happy Programming!