The last ClassLoader [#7] is the one which loads BlazeDS jars from WEB-INF/lib folder. Then as shown in exception stack trace if calls other Flex classes and HttpClient classes (which are available to the same class loader), but when it needs javax.net.ssl.SSLSocketFactory it fails.
I am not sure why this happens. If #7 cannot see this class, is it not true that it should go to its parent class loaders upto the Bootstrap class loader? And it is difficult to imagine why none of the classloaders are unable to load class from Java API.