Hi Chirag,
The error 633 denotes that the port is already in use or is not configured for Remote Access dial out. You may have to check if the VPN and dial out connection are trying to use the same port that is causing the issue. You may have to check the settings for the modem and change the port for your requirements.
Let us follow the steps given below and check if it helps.
Explicitly reserve the TCP port that is used for the VPN connection. To do this, follow these steps:
a) Press Windows key + R, type regedit.exe in the Open box, and then click OK.
b) In Registry Editor, locate and then click the following registry sub key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
c) On the Edit menu, point to New, and then click Multi-String Value.
d) Rename the multi-string value as "ReservedPorts," and then double-click ReservedPorts.
e) In the Value data box, type1723-1723, and then click OK.
f) Quit Registry Editor.
Registry disclaimer: This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
http://support.microsoft.com/kb/322756/
Hope this helps, if you have any further queries, feel free to post. We will be glad to assist you.