SQL server2012 Common Exception handling

Network-related cannot make sure TCP/IP is turned on via IP (127.0.0.1 or other native) connections

Open port 1433

Permissions related to the agent, either by changing the user with the highest privileges, or by assigning permissions to the user

Open SQL Server access to domain users

Windows Authentication mode is more secure because the Windows Authentication mode uses Kerberos (the term derives from the Greek mythology "three-head dog-the gate Keeper of Hell") protocol. The safest approach recommended by Microsoft.
However, Windows Authentication mode is used when the network access is controlled by a domain controller (a single machine is also included, using the NTLM protocol).

Errors that may occur during the Add process:

When you try to use SQL Server Enterprise Manager to provide a domain user or a domain group with access to a database, you may receive one of the following error messages:

Error 15023:user or role ' <name> ' already exists in the current database.-or-error 15024:the group ' <name> ' already exists in the current database.-or-error 21002:[sql-dmo]user ' <name> ' already exists.

Add specific steps:

1. Start Enterprise Manager.
2. Expand Microsoft SQL Server, and then expand the SQL Server group that contains your server.
3. Expand Security.
4. Select Sign in and right-click, and then click New Login.
5. In the SQL Server login Properties-New Login dialog box, type the full domain group or domain user name in the Name text box. For example, DomainName\UserName or DomainName\GroupName.
6. Click the Database Access tab.
7. Under Specify the databases that this logon can access, click to select the database that you want to allow this logon to access.
8. For all selected databases, replace the user name or group name under users with DomainName\UserName or DomainName\GroupName.
9. Click OK.

Other problems are trying to read or write protected memory. This usually indicates that other memory is corrupted. (System.Data)

The connection to the server has been successfully established, but an error occurred during the login process

(Provider:ssl provider,error:0-received a message exception, or is not in the correct format.) ) (Microsoft SQL Server)

The above two questions can be done with a command line. As follows:

netsh winsock reset

Thanks to Hedon solution, verified that the thunderbolt caused by the exception, uninstall all the products Thunderbolt, the problem is resolved.

Doubts are also before the use of thunder, perhaps the Thunder automatically updated some components caused, remember when win8 just out, Thunder also caused IE10 collapse. The specific principle is unknown, first of all.

Thanks Jaypgcool: Maybe Thunderbolt changed some of the Winsock settings, reset the Winsock on OK, command: netsh winsock reset

Refer to SQL server2012 issues when connecting to SQL Server 2008

Using mapped Windows domain users to access SQL Server

SQL server2012 Common Exception handling