You can compile your lazarus build If you remove the package links to sparta_Generics (<PackageName Value = "sparta_Generics" />) from sparta_mdi.lpk and sparta_toolsapi.lpk.Thank you for advice.
This problem is on the bug tracker: https://bugs.freepascal.org/view.php?id=35721
@af0815
With the next coming release a new docked form editor is comming.
which release?