Yeah, I thought that would do it as well, but no. For some reason that throws a Tabs.1 is null or not an object.
In the end I had to go routing around for all the spans with an id whos ending substring(length-9, length-1) contained 'TabPanel'.
I'm having a similar problem hiding the first tab on load to be shown when needed latter.
$find('<%=Tabs.ClientID%>').get_tabs()[0].set_enabled(false);
Works fine if wrapped in a function and called from a control. but if I try to lay it on the page to be called while loading :/ no success.
p.s. you missed your closing single quote ;) but I'll forgive you.