If the above does not help, the following should get you into act 4 (it works on one of my saves before killing the guardian mutant to trigger the cut scenes that should open the door).
Note: Normally, file swapping between saves can cause problems if the originals are not restored, since the different games were likely not played in the exact same order (mixing files can cause contradictions or conflicts with quests and/or quest items). However, since this location is at the very end of act 3, the files in question will be reset anyway, so this will not be a problem.
Procedure;
1 )
Download (199 KB) the zipped story files from my save after opening the entrance, and extract them to a temporary location.
2 ) Save your game under a new name, or make a copy of your latest save.
3 ) Move my story files from the temporary location into that new game folder.
4 ) Load this saved game, and click on the academy door. That should trigger the end of act cut scene, and bring your characters into act 4.
Each save is a separate subfolder in the '
..\Beyond Divinity\savegames' folder.