Hi Antonio,
did you finish your implementation project already by confirmed the activity “Perform Cutover”?
A consequence of this confirmation would be, that your system is switching to life usage, and a protection against parallel data migration in parallel to operational usage is being activated for all accounting objects (as well some other critical transactional data objects).
If that is the case, you will need a change project that contains this activity in its scope, after merging back the change project the corresponding migration objects will be open for migration - until this project is being confirmed, then the protection again becomes effective.
Regards
Michael