Can't connect to remote SQL server from some machines

Our web server uses SQL Server 2008 R2. I have one development machine that connects to it with the IP address through SSMS and when testing my aspx website. I have several other machines though that can't connect to the IP through SSMS. I'm getting this error:


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 the instance name is correct and the SQL Server is configured to allow remote connection.

(provider: Named Pipes provider:40-could not open a connection to SQL Server)
(Microsoft SQL Server, Error:53)

I've got TCP/IP enabled, port 1433 open, all of that. Remember that I can connect from one development machine, but not others.

Here are some of the things from my connection issue checklist

• Check for an alias on the machine that can't connect

• Check for firewall rules

• Check and make sure the SQL Server drivers on the machines that don't work are up to date.

• Try connecting with servername:port rather than just servername

• Try pinging the SQL Server IP address from the machines that can't connect.

StackExchange Database Administrators Q#104315, answer score: 4