I went into Plesk, into applications, to my installed WordPress application and it said that there was a newer version of WordPress available. I clicked on upgrade. I have never done this before. We have been working on this website for the past twelve months. In the past I have upgraded in the backend part of WordPress and WordPress would upgrade to the newer version of WordPress with no problems. Theme and plugin files did not disappear after upgrading to a newer version of WordPress. I have never upgraded WordPress to a newer version while inside of Plesk before. About a week ago, I upgraded WordPress in Plesk. Well, while upgrading Plesk ran into some kind of problem.It gave me this error message that says that some files are missing. After that, I was not able to get into my WordPress web builder or domain website either. I went into the file manager in Plesk and found theme and plugin files were missing.