Loopback Check

There are two methods to work around this issue that is designed to protect your system from bad internal code or malicious viruses.  Introduced on Windows XP SP2 and Windows Server 2003 SP1 to protect from what Microsoft calls to reflection attacks on your computer.  These are both well documented on TechNet.  https://support.microsoft.com/en-us/kb/896861
Typical syspton in Sharepoint is the windows security box to reappear after you type in a correct username and password.  To try again with no luck.  If you are getting this check the registry.

Creating a whitelist of good websites is the preferred method seen below.  However many SharePoint Admins just totally disabled the check in method 2 also noted below.

Method 1: Specify host names (Preferred method if NTLM authentication is desired)

To specify the host names that are mapped to the loopback address and can connect to Web sites on your computer, follow these steps:

1. Set the DisableStrictNameChecking
   registry entry to 1. For more information about how to do this, click the following article number to view the article in the Microsoft Knowledge Base:
   281308 Connecting to SMB share on a Windows 2000-based computer or a Windows Server 2003-based computer may not work with an alias name
   
2. Click Start, click Run, type regedit, and then click OK.
3. In Registry Editor, locate and then click the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0
   
   
4. Right-click MSV1_0, point to New, and then click Multi-String Value.
5. Type BackConnectionHostNames, and then press ENTER.
6. Right-click BackConnectionHostNames, and then click Modify.
7. In the Value data box, type the host name or the host names for the sites that are on the local computer, and then click OK.
8. Quit Registry Editor, and then restart the IISAdmin service.

Method 2: Disable the loopback check (less-recommended method)

The second method is to disable the loopback check by setting the DisableLoopbackCheck registry key.
To set the DisableLoopbackCheck registry key, follow these steps:

1. Set the DisableStrictNameChecking
   registry entry to 1. For more information about how to do this, click the following article number to view the article in the Microsoft Knowledge Base:
   281308 Connecting to SMB share on a Windows 2000-based computer or a Windows Server 2003-based computer may not work with an alias name
   
2. Click Start, click Run, type regedit, and then click OK.
3. In Registry Editor, locate and then click the following registry key:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
   
   
4. Right-click Lsa, point to New, and then click DWORD Value.
5. Type DisableLoopbackCheck, and then press ENTER.
6. Right-click DisableLoopbackCheck, and then click Modify.
7. In the Value data box, type 1, and then click OK.
8. Quit Registry Editor, and then restart your computer.