Please use the following steps:

You will need the create the following registry Key (REG_DWORD) under HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Sstpsvc\Parameters
Setting the key value of 1, will prevent it from checking.

More detailed info below:

Registry subkey: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Sstpsvc\Parameters
Registry entry: NoCertRevocationCheck
Data type: REG_DWORD

You can use this registry entry to enable or to disable the SSL certificate revocation check that the VPN client performs during the SSL negotiation phase. Certificate revocation check will be performed if the value is set to 0. If the value is set to 1, certificate revocation check will be skipped. Notice that you should set this value to 1 only for debugging. Do not set this value to 1 in your production environment. By default, certificate revocation check is performed.