Possible cause for a failure to establish the L2TP over IPSec tunnel between the AR and PC running Windows 7 or Windows XP

The system registry may be not modified.
Use Windows 7 as an example. Modify the Windows registry and do not use the digital certificate. The method is as follows:
1. Choose Start > Run and enter regedit to open the registry.
2. Access HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\RasMan\Parameters , and right-click the blank area on the right and choose New > DWORD (32-bit) to generate a new file named New Value #1.
3. Select New Value #1, right-click Rename to rename the file name ProhibitIpSec.
4. Select the ProhibitIpSec file, and right-click file and select Modify.
5. Set Numerical Data to 1 and set Cadinality to 16 hexadecimal in the displayed Edit DWORD�?2-bit�?value dialog box.
6. Restart the PC to make the configuration take effect.

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