Tasker - Advance Settings - Export App Package Name?
What are you putting in for the package name that it doesn't like? Beginner mode vs non-beginner mode shouldn't matter.

Package name has to have at least one . in it to be valid.  Usually you can just use your email backwards along with a unique name for the app.  Say your email is someone@gmail.com and you're trying to export an app you want to call myapp.  The package name could be com.gmail.someone.myapp.