When I experienced this error in Visual Studio,
“A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)”
...it was during the execution of the following C# code, which was attempting to obtain my SQL Server data to display it in a grid. The break occurred exactly on the line that says connect.Open():
using (var connect = Connections.mySqlConnection)
{
const string query = "SELECT Name, Birthdate, Narrative FROM Friends";
using (var command = new SqlCommand(query, connect))
{
connect.Open();
using (var dr = command.ExecuteReader())
{
while (dr.Read())
{
// blah
}
}
}
}
It was inexplicable because the SQL query was very simple, I had the right connection string, and the database server was available. I decided to run the actual SQL query manually myself in SQL Management Studio and it ran just fine and yielded several records. But one thing stood out in the query results: there was some improperly encoded HTML text inside a varchar(max) type field within the Friends table (specifically, some encoded comment symbols of the sort <!-- lodged within the "Narrative" column's data). The suspect data row looked like this:
Name Birthdate Narrative
==== ========= ==============
Fred 21-Oct-79 <!--HTML Comment -->Once upon a time...
Notice the encoded HTML symbol "<", which stood for a "<" character. Somehow that made its way into the database and my C# code could not pick it up! It failed everytime right at the connect.Open() line! After I manually edited that one row of data in the database table Friends and put in the decoded "<" character instead, everything worked! Here's what that row should have looked like:
Name Birthdate Narrative
==== ========= ==============
Fred 21-Oct-79 <!--HTML Comment -->Once upon a time...
I edited the one bad row I had by using this simple UPDATE statement below. But if you had several offending rows of encoded HTML, you might need a more elaborate UPDATE statement that uses the REPLACE function:
UPDATE Friends SET Narrative = '<!--HTML Comment -->Once upon a time...' WHERE Narrative LIKE '<%'
So, the moral of the story is (at least in my case), sanitize your HTML content before storing it in the database and you won't get this cryptic SQL Server error in the first place! (Uh, properly sanitizing/decoding your HTML content is the subject of another discussion worthy of a separate StackOverflow search if you need more information!)
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