[quote user="Zhen Li"]I can not find "MSGBOX_ICON_CRITICAL" definition[/quote]
The design of MDL relied on a huge number of #define statements in the public namespace.
The MicroStationAPI rationalises many of those into enumerations.
Try the MessageBoxIconType enum, which you'll find in NotificationManager.h...
#include <NotificationManager.h> mdlDialog_openMessageBox(DIALOGID_MsgBoxOK , L"LA Solutions", MessageBoxIconType::Critical);