User defined base class linked with 2 symbols gives Error #1034: Type Coercion failed

Hi, I have two movie clips in the library linked to the same base class, Container, with different class names defined in Properties. These clips each contain (nest) several other clips that are also linked to another base class, Contained. Is there something else that needs to be done to deal with nested clips like this? I’m not certain that nesting is an issue, but in a scenario with different symbols I could not replicate the problem. I’ve attached a simplified version of the problem .fla with the 2 .as files. I’m using the latest version of CS3. The error is: TypeError: Error #1034: Type Coercion failed: cannot convert [email protected] to Contained_PosteriorLeft.