Unable To Connect Establish Connection To VPN Error

My Dear friends,
I am receiving this particular error while connecting to my VPN Server. If anyone knows how to solve this error, please do reply When I click the redial button, it retries to connect to the VPN Server but after 30 seconds it again displays the same error.

Error Connecting
Error 800: Unable to establish VPN connection.
The VPN server may be unreachable, or security parameters may not be configured properly for this connection.
I don’t understand how this error can be removed or resolved.
It says that a security parameter might not be configured. Now what is this security parameter?
If you know how to configure this security parameter, then please reply to this question as I am in a hurry to get this issue resolved.
