Cookies with Flash Remoting?

I’m using amfphp and I have a service which needs to return the value of a cookie, previously set by my application. If I try and echo the cookie anywhere else, it is returned as expected, but when trying to call it from my amfphp service, it gets returned as ‘null’, even though I know it has been set.

If I ask the service to return a simple string, it works fine, so as far as I can tell, it’s not a problem with the set up.

Any insights?