Thanks Tuur, this code fail with any command, as the "&" char is not possible.
This action works fine:
<action name="mycode">
popup('iframe', 'index.html?startactions=trace('hello')', 800, 600, false);
</action>
but this not:
<action name="mycode">
popup('iframe', 'index.html?starscene=scene4&startactions=trace('hello')', 800, 600, false);
</action>