I received a "Could not move AST class 'XImpl'." exception (where 'X' is the name of the metaclass/nonterminal and 'Impl' is Ecore's suffix for implementation classes). What could be a cause?

There are multiple potential reasons for this:

1. There’s a mismatch between the Ecore metamodel and the JastAdd AST grammar, i.e., 'X' does not exist in both models (due to a typo, for instance).
2. The system was not able to perform the rename refactoring to obtains the 'Impl' class, for example due to some errors in the 'X' Java file itself or in dependent artifacts in the workspace. Another potential reason are locks or write protection of the respective Java file.
3. The renamed class has too many errors to perform the move refactoring.
4. There is an issue in the path setup (something went wrong when creating the move target location or the move target is wrong)