I found this article that give me a resolution of the problem described in the object.
When it say:
1. Delete the information in the System Files folder
it means that I must DELETE ALL THE FILES (folder, zip files, XML Document files and Analysis Services Dimension files) in that folder?
They are very important files and I have to be sure, even if the point n. 3 says that "The Full Process" will rebuild all of the dimension files which were previously stored in the System Files folders"
Thank you in advance.