PSIsafe Troubleshooting: Issue 02.03: If clicking Login button, you receive error after 90 seconds

Problem: 

If on clicking the “Login” button, you receive this message after about 90 seconds:

Unable to connect to server. Reason: 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: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

Solution: 

1) Make sure your server name is correct, e.g., no typo on the name.
2) Make sure your instance name is correct and there is actually such an instance on your target machine. [Update: Some application converts \\ to \. If you are not sure about your application, please try both Server\Instance and Server\\Instance in your connection string]
3) Make sure the server machine is reachable, e.g, DNS can be resolve correctly, you are able to ping the server (not always true).
4) Make sure SQL Browser service is running on the server.
5) If firewall is enabled on the server, you need to put sqlbrowser.exe and/or UDP port 1434 into exception.
6) If it is ONLINE, Restart SQL Browser service.
Once you are done the steps, you should not see this error message anymore. You may still fail to connect your SQL server, but error message should be different and you have a different issue now. [Update: If it still fails, you may replace server\instance with tcp:server\instance and/or np:server\instance and see if it succeeds with either TCP or NP protocol. That way, you can isolate the issue a little bit. ]
There is one corner case where you may still fail after you checked step 1)-4). It happens when a) your server is a named instance on cluster or on a multi-homed machine, and b) your client is a Vista machine with Firewall on.
There is a tool online which could be very helpful for users to isolate issues related to this error message. You can download PortQry from http://support.microsoft.com/kb/832919, run "portqry.exe -n yourservername -p UDP -e 1434" If this command returns information and it contains your target instance, then you can rule out possibility 4) and 5) above, meaning you do have a SQL Browser running and your firewall does not block SQL Browser UDP packet. In this case, you can check other issue, e.g. wrong connection string.