1) What happened
When building for Flash, I get this error

Invalid generic argument, specifically -
Failed to convert type 'ICS_Unity_IO_Http.TraceyTest3': Invalid generic argument ''.

This happens when trying to convert open generics to Flash, which I'm pretty sure AS allows.

2) How can we reproduce it using the example you attached

Put this line of code in any C# file -

IList list = (IList)Activator.CreateInstance(typeof(List<>).MakeGenericType(typeof(string)));

This is a trivial example, but when you start passing in the type to create a generic list out of, especially during serialization, it becomes much more useful...think json serialization, etc.