QML Extension Plugin failed to load

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Hello, everyone. I installed the Qt SDK v1.2.1 for windows recently, then I created a new 'Custom QML Extension Plugin', and use 'Charles' for project name, object class-name and URI.

After compiled the plugin(release), I put the Charles.dll(the plugin) and the qmldir file into a new QtQuick UI project directory,and I imported the plugin.Then I got an error:

@Qml debugging is enabled. Only use this in a safe environment!
file:///E:/Desktop/QT/UI/UI.qml:4:1: plugin cannot be loaded for module "": The plugin 'E:/Desktop/QT/UI/Charles.dll' uses incompatible Qt library. Expected build key "Windows mingw debug full-config", got "Windows mingw release full-config"
import "./" @

qml file(UI.qml):
@import QtQuick 1.1
import "./"
Rectangle {
width: 360
height: 360
Charles{
id:logic
}
}@

qmldir:
@plugin Charles@

I remember tried this in August 2011,using sdk 1.1.2 and worked well. oh my:-(
It seems that qmlviewer found the plugin but unable to load it.I use the same Qt version(4.7.4 for desktop-MinGW 4.4)for the plugin and QtQuick UI project.

***Earlier today,I found that when I go to project tab and change Qt version(run settings for the QtQuick UI project)from desktop to simulator,the plugin load successfully. Then I change back, the error reoccur...

Anyone can help me?thanks in advance :-)