I do not own the Gog version of the game, but the original boxed 2-CD-Version.

I have reached Cet's pyramid and placed the missing tablets into its respective slots. But the doors to the inner pyramid do not open. The narrator hints at the fact, that something is stuck. And while the first inserted tablet to the right can be clicked on without a response from the game, clicking on the two others (the one on the left and the second to the right) gives the message "The tablet is not working".

I haven't found anything about this behaviour and haven't got the slightest idea, what is to be done. I thought that maybe the order of inserting the tablets may be of importance. But that does not seem to be the case, because I varied the order and get the same result.

Has anybody experienced something similar and can help me solve this problem?

Problem is solved. The pyramid does open. It just takes about 60 - 70 minutes, until the outer doors are closed, the pyamid is loaded and the inner doors start to open (which takes another 20 - 30 minutes).