don't have the "swc" option in publish settings dialog

Hi. I'm trying to use flash cs5 to build a custom preloader for a flex4 app. I'm a complete newbie to flash cs5

I'm trying to follow this example:

http://www.leavethatthingalone.com/blog/index.cfm/2009/11/11/Flex4Cust omPreloader

but I can´t publish my fla into an swc file (I don't have that checkbox in my publish settings dialog)

So I never get to the Linkage box to check "Export for Action Script", "Export in Frame 1" and add my class and base class names.

I'm pretty sure I'm just being blind... Can't find that.

Could someone give me a hand? Online help proposes to publish as swc but I don't have that option in publish settings.

Sandra