Here is my Interface.xml file:
<Interfaces xmlns="urn:msgplus:interface" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsichemaLocation="urn:msgplus:interface
C:\PROGRA~1\MESSEN~2\Scripts\PlusInterface.xsd">
    <Window Id="WndTest" Version="1">
        <Attributes>
            <Caption>Test Window</Caption>
        </Attributes>
        <TitleBar>
            <Title>
                <Text>Hello!</Text>
            </Title>
        </TitleBar>
        <Position Width="180" Height="75"/>
        <DialogTmpl/>
        <Controls>
            <Control xsi:type="StaticControl" Id="LblTop">
                <Position Left="10" Top="10" Width="150"/>
                <Caption>Hello world!</Caption>
            </Control>
            <Control xsi:type="ButtonControl" Id="BtnClose">
                <Position Left="112" Top="25" Width="50"/>
                <Caption>Close</Caption>
            </Control>
        </Controls>
    </Window>
</Interfaces>
Here is my Script:
function OnEvent_Initialize(MessangerStart)
{
    var Wnd = MsgPlus.CreateWnd("Interface.xml","WndTest");
}
When I run it nothing happens, when I replace the Interface.xml with another file from someone elses script and change the window IDs the window opens... I need help. Note that the file is called Interface.xml

I remember something with a simluar problem. Believe you have to save the .xml files as Unicode. Can someone confirm?

Yes, when you save the XML, you must save it as unicode or the window will not appear.

Thank you ! It works now

I made a window for you which is better than yous. I hope that helps.

Edit : Opps! Im late but this is a better example of a window .