Flex 2 with AS 3.0: Transitions code compilation error

Question

I just bought "The Essential Guide to Flex 2 with
ActionScript 3.0. (Friends of Ed 2007) In order to work through the
examples, I downloaded Flex 3.0 beta. Its been going well ... until
starting the exercises on transitions.
I've narrowed the problem down to the "relativeTo" attribute
of the AddChild class. This snipped builds and runs fine:
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="
http://www.adobe.com/2006/mxml"
layout="absolute">
<mx:states>
<mx:State name="bookDetails" basedOn="">
<mx:AddChild creationPolicy="all" position="lastChild">
<mx:FormItem id="isbn" label="ISBN: 1590595432" />
</mx:AddChild>
</mx:State>
</mx:states>
<mx:Panel title="Book" id="book"
horizontalScrollPolicy="off" verticalScrollPolicy="off">
<mx:Form id="bookForm">
<mx:FormItem label="Foundation XML Flash"
fontWeight="bold" />
<mx:FormItem label="Sas Jacobs" fontStyle="italic" />
</mx:Form>
<mx:ControlBar>
<mx:LinkButton label="Book Details" id="bookLink" />
<mx:Spacer width="100%" id="spacer1" />
<mx:Label text="Book Title" id="title" />
</mx:ControlBar>
</mx:Panel>
</mx:Application>
However, as soon as I add relativeTo, e.g:
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="
http://www.adobe.com/2006/mxml"
layout="absolute">
<mx:states>
<mx:State name="bookDetails" basedOn="">
<mx:AddChild relativeTo="{bookForm}" creationPolicy="all"
position="lastChild">
<mx:FormItem id="isbn" label="ISBN: 1590595432" />
</mx:AddChild>
</mx:State>
</mx:states>
<mx:Panel title="Book" id="book"
horizontalScrollPolicy="off" verticalScrollPolicy="off">
<mx:Form id="bookForm">
<mx:FormItem label="Foundation XML Flash"
fontWeight="bold" />
<mx:FormItem label="Sas Jacobs" fontStyle="italic" />
</mx:Form>
<mx:ControlBar>
<mx:LinkButton label="Book Details" id="bookLink" />
<mx:Spacer width="100%" id="spacer1" />
<mx:Label text="Book Title" id="title" />
</mx:ControlBar>
</mx:Panel>
</mx:Application>
Flex Builder 2 gives me the following error:
Type was not found or was not a compile-time constant.
Thinking this might have been a bug with Flex 3.0, I
uninstalled then installed the most recent release of version 2. I
still get the same problem. Any ideas?

Answer 1

Another possibility is that you used some kind of transition for the object but didn't name it in all of the keyframes.  When you transition an object in a timeline tween and don't name it in the first keyframe, the latter keyframes adopt that lack of a name event though you might assign a name in them.
What you should do is go into your Publish Settings and in the Flash section select the option to Permit Debugging.  This will add a line number following the frame number in the error message.  Once you know which line is causing the problem, try tracing the object that is in that line.  You will most likely find out it is null, and it will be because of one of the reasons I've mentioned (I don't think I forgot any others, but it's possible).