The error dialogue won't go away.
Workflow: There are two composite actors, one called CompositeActor1 on the top level, another called CompositeActor2, in CompositeActor1. There are two String Parameters: one called p1 on the top level, another called p2 with value '$p1/l', in CompositeActor1. p2 is used in actors in CompositeActor1, such as expression, file open.
1) Open the whole workflow,
2) Open CompositeActor1,
3) Open CompositeActor2,
4) Close CompositeActor2,
5) Delete CompositeActor2,
6) Change the value of p1.
There will be an error saying that: "Error evaluating expression: $p1/l in .CompositeActor2.p2 Because The ID p1 is undefined."
There is no way to close the error except closing Kepler by force, which will lost all unsaved modification.
I found the bug with Kepler version 16865 and ptolemy version 52661, but I think this bug is always there.
I attached the workflow and error dialogue.