What
@RunRudolf says about multiple Timeline versions in the scene makes sense, do check for that. Older versions of Timeline don't have a "Play segment" option and that would explain the error.
As for triggers, the trigger system is a base VaM function, doesn't matter usually if the trigger is used in VAMStory or any other atom/plugin. I don't think the problem is in VAMStory but on the trigger itself. Is there a "ant" segment in that Timeline? Maybe you
renamed it or
deleted it but the trigger still keeps the old information. Delete the trigger and make it again to be sure it's correctly set.
Scene suggestion:
Instead of using "Anna:" in the text, you have the option to include a avatar image to show the person. This is a really cool feature that makes your story dialogue look more polished.