System.Data.SqlClient.SqlException in .NET 1.1 and 2.0

I recently had the privelege to explore a SQL 2000 to SQL 2005 upgrade for one
of our Web applications, and in the same breath an upgrade from
the .NET 1.1 framework to .NET 2.0...

I'll talk about the specifics that I learned during the SQL upgrade another time,
but I ran into only one issue during my 1.1 to 2.0 upgrade process. The issue wasn't
even really an .NET framework issue.

Long story short, my lesson learned was essentially establish that the app works
before the upgrade. Duh, can you say BASELINE? What threw me for a loop
which led me astray is that the .NET 2.0 led me to believe that I had a SQL 2005 configuration
issue:

Error With .NET 2.0
Exception=System.Data.SqlClient.SqlException: 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)

To troubleshoot, I rolled back to .NET 1.1 with SQL 2000 and saw:

Error With .NET 1.1

Exception=System.Data.SqlClient.SqlException: SQL Server does not exist or access
denied.

Interesting, so I didn't have a SQL 2005 OR .NET 2.0 problem. The issue? I learned
that the above errors occur when:

1. SQL not started (duh, that wasn't my problem though)
2. IPSEC configured incorrectly (my problem)

The fix:
1. Start SQL Server
2. Configure IPSEC so that the servers  can be pinged successfully
in both directions (Web server to SQL and SQL to Web server)

Why am I telling you all of this? Because I have nothing better to do right now. Err...
Or...While Googling on my SQL 2005 error I found some great SQL Server 2005 connection
troubleshooting links. If you're stuck with SQL 2005 connection issues here are
three some references to check out:

Troubleshoot
Connectivity Issue in SQL Server 2005 - Part I

Troubleshoot
Connectivity Issue in SQL Server 2005 - Part II

Troubleshoot
Connectivity Issue in SQL Server 2005 - Part III

Even Better,
just use this site/search