The museum is the place with the death masks, right? There's an area there that it's fairly easy to miss.
Are you sure you visited both areas in there ? The one with the mask and the one with the cloak ? Click on everything in both the left and right side areas, also on the reception area, and then try to talk to the receptionist again
Edit: Ah, you figured it out ;)

Is that chapter 4? The call Gerte tells you about when you enter the castle ?

Yes. I must have clicked through it not realizing. When I try the card on the phone she says he'll call if he finds anything.

Ah, you skipped that cut scene with Gerde then. I don't know if that would prevent you from calling the professor, maybe you still need to do something before being able to call him. If you still have 'things' you can do in other places, maybe do them and then try to call the professor again. Try talking to Gerde to see if there are any more dialogue lines from her.

I have the same problem: Gerde does not tell me about a missed phone call, hence I cannot complete the chapter. I checked out some of the walkthroughs available, visited the museums at least three times, Neuschwanstein is not blinking on the map. I even started the game again and now I am stuck at the same spot. Is it a bug? I would be very grateful for any hint!

You are SUPPOSED to miss the phone call from the professor and learn that from Gerde. It's okay, you can call him back.

If you're not getting that cut scene, then you missed something at the museums. Be sure to look at everything, including the display case below the painting that reminded Grace of her dream, and listen to the tape for everything at the castle. Also, after you've looked at the wolf panels in the castle, go back and ask Georg about them.

You can also go back and ask Huber and the Smiths about things as you learn new stuff.

Hey
Tanks for your Response. I know I am supposed to miss the call but he never does call - Graces sais "he will call when he's got something" when I try. I looked at everything including the panels and the wolf painting - I even went through several walkthroughs and did everything described in there. I exhausted every topic with Huber, the Smiths AND Wolfgang. Seriously lost here.

I have the same problem I can't get the professors call and I can't get book publisher ether.
I have been back to all the museums 100/s times and i don't think I have missed anything
but the way its laid out who knows . Maybe I need to restart too
I have played the chapter over now 3 times and I never get more that 321 score and can't go into the next chapter.
This games is running on Windows 7 and it is not installed on the C: drive. I have see in other adventure game where they didn't load a necessary file until I put the in the task bar I fixed them by reinstalling them in program files.
Do you think I need to do that or is there something else I could have missed.