Is this the version of the game from GOG or an old CD version of the game? The original CD version had a patch that you can download from here
http://www.gamefront.com/files/901869/gk2pat11.zipAccording to the Readme for the patch, one of the things it does is to Correct the "Out of Memory" message at Schloss Ritter in Chapter 4.
This is the list of everything it fixes:
1. Corrects "Out of memory" message at Schloss Ritter in Chapter 4.
2. Corrects "Error 99: Error Loading Resource 122v56" that occurs when switching to CD #2.
3. Fixes "dead end" that occurs when player exhausts dialogue with Leber before visiting Ubergrau's office for the first time and then can't get back to Leber to ask about "Black Wolf".
4. Fixes problem where Neuschwanstein border does not stop blinking even after player has heard every tour tape.
5. Fixes problem where Georg does not have "Lost Opera" topic if player hasn't clicked on "Letter to Conductor" in the Museum but has exhausted topics with Frau Miller, then cannot get back to the Museum.
6. Allows Grace to get holy water only once.
7. Corrects "thrashing" or continuous hard drive or CD drive reads.