what happens when you compile your swf and click the buttons?
Do you get an error
Do you get a warning
Does the browser attempt to open a site?
your code looks good.
I don't get an error or warning but nothing happens. My browser doesn't attempt to open anything.
Do you happen to have any kind of rollover code tied to anything that is containing the buttons? I don't see the sense in having Flash buttons unless you have some form of animation associated with them, possibly triggered by rollover interactions. If so, the rollover may be blocking access to the on(release) interaction.