Dear Maru, I will try! Thanks.
Before I would like to exclude more easy ways. I can see MaterialLibrary folder in this path. "C:\Users\Giovanni\AppData\Local\CoronaRenderer"; Should I try to copy (or cut) and paste this folder in the following path: C:\Program Files\Corona? This is the path that is indicated in the support article.
Moreover I have to say that sokme days ago due to a Kernel Power error (41) of Windows I had to reconnect the path of Corona for 3Ds Max as descripted on solution 4 of this article:
https://support.chaos.com/hc/en-us/articles/4526221582993-Corona-is-not-showing-up-as-available-renderer-and-is-not-present-on-the-plugins-list-3ds-MaxBefore I updated Windows but I did not followed all the previous solutions (because the n.4 seemed the best). Maybe I could try to use solution n.4 also for this problem with Material Library missing or I could try to re-do starting from solution 1 in the article? Thanks!