Qml plugin cannot be loaded in my qml project

[nan3113]

in qml file of qml project:
import com.groveil.tools 1.5
when I run it in creator, it outputs:
plugin cannot be loaded for module "com.groveil.tools ": Cannot load library D:/brooks/com/groveil/tools/Button.dll: ?ò2?μ????¨μ??￡?é?￡
in com/groveil/tools directory, there's a qmldir file,contents is simple like this: plugin Button
plugin C++ implementation is also simple.

@
class BUTTON_EXPORT ButtonPlugin : public QDeclarativeExtensionPlugin
{
Q_OBJECT
public:
void registerTypes(const char *uri)
{
Q_UNUSED(uri);
Q_ASSERT(QLatin1String(uri) == QLatin1String("com.groveil.tools "));

qmlRegisterType<Button>("com.groveil.tools ", 1, 5, "Button");
}
};

Q_EXPORT_PLUGIN2(Button, ButtonPlugin);
@

I don't know what's wrong?

---

I find if I create a plugin which don't rely on other dlls, it can be loaded;
here my plugin relys on another dll, even though I copy the another dll into the same directory of plugin, but plugin still can't be loaded.
[EDIT: code formatting, please wrap in @-tags, Volker]