Does the connection string use machine name, IP address, etc.?

Have you considered using SQL authentication instead of Windows
authentication?  Are you sure ports 1433 and 1434 are reachable between
machines (you can test this by trying to telnet)?  This could be blocked by
Windows-based firewall on either or both machines, or maybe by a hardware
firewall within your network.

By default, 2005 is a little more locked down than 2000.  This is because
slammer taught them a few things about leaving SQL services wide open and
exposed.  I assume you have enabled remote connections for both TCP/IP and
named pipes via the surface area configuration tool?

try adding ",1433" to the end of the connection string, I had this
exact same issue before, I spent a while trawling the net and found
out why I might need to do this (something about firewalls and
callback ports and lots of big interweb words), the reasonmade total
sense at the time but now eludes me.

Hi Gary,
There are many factors which would cause the connection error. Look at your
issue, I recommend that you first check the following conditions and let us
know the results:
1. Check if remote connections for both TCP/IP and Named Pipes is enabled
   Click  Start->All Programs->Microsoft SQL Server 2005->Configuration
Tools->SQL Server Surface Area Configuration->Surface Area Configuration
for Services and Connections, expand <instance name>->Database Engine and
select Remote Connections, then you can find "Local and remote connections"
at the right pane, select "Using both TCP/IP and named pipes" if it is not
selected.

2. Check if the listening port of your SQL Server instance is blocked.
   Click Start->All Programs->Microsoft SQL Server 2005->Configuration
Tools-> SQL Server Configuration Manager->SQL Server 2005 Network
Configuration->Protocols for <instance name>, ensure that the TCP/IP
protocol and Named Pipes protocol are enabled, then double click the TCP/IP
protocol, switch to the IP Addresses tab, and you can find the in use TCP
port at the bottom of the IPAll section.
   Then run firewall.cpl from command line to see if the TCP port is added
to the Exceptions list.

3. Check if you can telnet to your SQL Server 2005 listening TCP port from
your client machine.
    Assume that the TCP port is 1433, you can run "telnet <remote server
name> 1433" to see if you can connect to the endpoint.

4. Check if the SQL Browser services is started
   Run Services.msc from command line to see if SQL Browser Services is
started. If not, start it and open your firewall to add the program
(sqlbrowser.exe) to the Exceptions list.

5. Check if you can manually connect to your SQL Server instance via a SQL
login.
   To do this, you may first set your SQL Server 2005 Server
Authentication mode to "SQL Server and Windows Authentication mode" which
you can find at Server Properties window by right clicking the server name
and clicking Properties on the shortcut menu in SQL Server Management
Studio. Then run "osql -S <servername>\<instancename> -U <username>
-P<password>" from command line.

Also I would like to ask you the following questions:
1. What is your connection string in your ASP.NET applicationi?
2. I am not familiar with ASP.NET, however could you please let me know why
you set machinename/aspnet and NT AUTHORITY\NETWORK SERVICE as the db owner
of your database?

Look forward to your response. Please feel free to let us know if you have
any other questions or concerns.

Best regards,
Charles Wang
Microsoft Online Community Support
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Delighting our customers is our #1 priority. We welcome your
comments and suggestions about how we can improve the
support we provide to you. Please feel free to let my manager
know what you think of the level of service provided. You can
send feedback directly to my manager at: msdnmg@microsoft.com.
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I assume you are yalking the error message when connecting to a SQL
Server2005/Express fails.

Since SQL Server2005/express is the first version of SQL Server having
default installation disabled remote connection, thus, MS made such "extra
detailed" error message. But you should not limit your thought in that box,
especially when you already know that you have enabled the SQL
Server/Express' remote connection (through "SQL Server Surface Area
Configuration"). That is, unless you haven't enable remote connection, then
do it. I f you have done that (no harm to double-check, though), you need to
look into something else, such as wrong server/database name, or wrong port
number in ConnectionString, current user does not have logging
permission..., just regard that error message as connection falure message
and do your trouble shooting.

That is, disabled remote connection is just one of the reasons you cannot
connect to SQL Server, there are more other reasons you need to learn. That
error message is more useful to users who were familiar to SQL Server2000 to
give them an extra prompt to the new default SQL Server 2005 setting.