So, in the form private I declared:
fScrolling : boolean;
fMouseDownX, fMouseDownY, fOrigViewX, fOrigViewY: Integer;
In OnMouseDown :
if (Button = mbRight) then begin
fScrolling := True;
fMouseDownX := X;
fMouseDownY := Y;
fOrigViewX := ImageEnView1.ViewX;
fOrigViewY := ImageEnView1.ViewY;
end;
That solved it.
Thanks