This can happen when the encryption that your computer uses does not match the encryption used by the VPN server. To change the encryption settings so that your computer uses the recommended setting of 3DES, follow these steps:

1. Open Network and Sharing Center.

2. Click Connect to a network.

3. Right-click the VPN connection, and then click Properties.

4. Click the Security tab, click Advanced (custom settings), and then click Settings.

5. In the Advanced Security Settings dialog box, under Data encryption, select Maximum strength encryption (disconnect if server declines), and then click OK twice.

6. Click Connect to try connecting again.