There are two possible causes:
If you change the TTS Mode ID of the default character and then allow the user to change the default character through ShowDefaultCharacterProperties, AgentSvr will crash.
This problem has been fixed in the Windows 2000 and Windows XP operating systems. To avoid the crash on other platforms, you should either not allow the user to change the default character after you change the default character's TTS Mode ID, or do not use the default character in your application or webpage.
If your application does not use Microsoft-supplied Agent characters, make sure that your customized character uses a palette with a full palette of 256 colors. For more information see the Designing Characters for Microsoft Agent document.