Problem with ribbon buttons and macros

Question

I made my first custom Ribbon tab, with the following code:
Code Block
<customUI xmlns="http://schemas.microsoft.com/office/2006/01/customui">
    <ribbon>
        <tabs>
            <tab id="Adnet" label="Adnet" insertAfterMso="Add-ins">
                <group id="NetVision" label="NetVision alati">
                    <button id="Brisanje" label="Brisanje" size="large" onAction="Brisi()" imageMso="Delete" />
        </group>
            </tab>
        </tabs>
    </ribbon>
</customUI>
That puts a new tab and a button in my ribbon. But when i click the button, it executes the Brisi() macro twice (?!) and then it shows a mesage box with only "400" written in it (link to picture of message box). If I run the macro alone, without the button, it executes fine.
What's the problem?

Answer 1

Excel is the program in question.
I made an add-in with one module and with the altered ribbon. In the module there is a Sub routine Brisi() and it has the following code:
Code Block
Sub Brisi()
    Debug.Print ("Opened.")
End Sub
When I click the button, the debug window shows "Opened." twice. And the before mentioned "400"
When I remove the "()" from the .xml it results in this.
I'll put the whole extension on the net, and then You can try. I would be extremely grateful