Basic4ppc "fills in" all your event variables with a reference to its event handler that handles events from external libraries. This handler is of type EventHandler and so that is what your event variables must be declared as
Might be as well to check all your other event declarations in the other buttons as well.
B4X:
public event EventHandler Click;
private object[] eventObject;
public event EventHandler MouseDown;
private object[] eventObject1;
public event MouseUp;
private object[] eventObject2;