SQL Server does not exist or access is denied

"[Dbnetlib] [connectionopen (connect ().] SQL server does not exist or access is denied" occurs when the SQL server remotely connects to the database. There are many reasons, which are generally checked:

1. Firewall;
2. port 1433;
But today we find that the following situations can also cause this problem.
Exclusion Process:
1. Check that the firewall settings and port 1433 settings are correct;
2. If an error "cannot find the network path" is reported, ping its IP address first. If the ping fails, check whether it is connected to the network or the network connectivity is normal. Check whether the firewall is enabled or the corresponding port is blocked. If the IP address can be pinged but the computer name of the target machine cannot be pinged, check whether the network name resolution is correct. For how to diagnose the name resolution problem, you can first check whether there is a problem with all client machines or a machine. If the name resolution of all machines is incorrect, you need to check the DNS or WINS server on the network. If there is a problem with only one machine, you need to check the hosts and LmHosts files first. If yes, you can re-register the DNS name (ipconfig/reisterdns ).
---- Normal;

3. If "xxx computer cannot be accessed, you may not be authorized to use network resources. Please contact the administrator of this server to check whether you have access permissions. "The error may be that the computer's security settings have been changed, and the target computer cannot be accessed. Follow these steps:
--- Solve this problem through the following methods:

A. open "my computer", choose "Tools"> "Folder Options"> "View" from the menu, and clear the "use simple file sharing (recommended)" option.

B. right-click "my computer", select "manage", select "local user and group"-> "user", right-click the Guest user, and select "attribute ", clear the "Account Disabled" option.

C. click Start> Run and enter secpol. MSC, select "Local Policy" on the left-> "User power assignment", and double-click "access to this computer from the network" on the right to ensure that there is everyone, double-click "Deny access to this computer from the network" on the left to make sure it is empty.

D. select "Local Policy" on the left-> "Security Options",. confirm "network access: the sharing and security mode of the Local Account" on the right is "classic"; B. confirm "Microsoft Network Customer: enable digital signature for communications (always)" on the right is "disabled"; C. confirm "Microsoft Network Customer: enable digital signature for communications (if Server permits)" on the right is "enabled"; D. confirm "Microsoft network server: enable digital signature for communications (always)" on the right is "disabled"; E. check that "Microsoft network server: enable digital signature for communications (if allowed by the server)" on the right is "enabled ".

4. Use ODBC to connect. The result is OK.