TAPI 3.X and Windows XP. Must see this why CallDisconnect is not working. Its really a micro soft Bug.

SYMPTOMS
Telephony API (TAPI)-based applications may stop responding in a Microsoft Windows Server 2000-based telephony server. Additionally, you cannot disconnect telephone calls even though the remote party has disconnected.

This problem occurs if the following conditions are true:
• A telephone call is being disconnected.
• The server is located in a large telephony server call center.
• The telephony server has more than one CPU.


CAUSE
This problem occurs because of a deadlock condition between the lineClose function call and the lineDeallocateCall function call.


RESOLUTION
Hotfix information
A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that this article describes. Apply it only to systems that are experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:
http://support.microsoft.com/contactus/?ws=support (http://support.microsoft.com/contactus/?ws=support)
Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.
Prerequisites
To apply this hotfix, you must have Windows 2000 Service Pack 4 (SP4) installed on the computer.
Restart information
You must restart the computer after you apply this hotfix.
Hotfix replacement information
This hotfix is not replaced by any later hotfix.
File information
The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.
File name File version File size Date Time Platform
Tapisrv.dll 5.0.2195.7111 176,400 26-Sep-2006 11:52 x86


STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.


MORE INFORMATION
For more information about Microsoft Windows Server 2003 version of this hotfix, click the following article number to view the article in the Microsoft Knowledge Base:
924050 (http://support.microsoft.com/kb/924050/) Telephony API-based applications stop responding and you cannot disconnect telephone calls on a Windows Server 2003-based telephony server
For more information about the terms that are used to describe software updates, click the following article number to view the article in the Microsoft Knowledge Base:
824684 (http://support.microsoft.com/kb/824684/) Description of the standard terminology that is used to describe Microsoft software updates