Wordpress - Why Did My Plesk break My Wordpress Website?

My website randomly broke while I was upgrading my Wordpress website and builder from Wordpress version 3.4 up to 3.5. You can upgrade in the Wordpress builder, in the backend interface of your website and you can upgrade in the server side. My server is with GoDaddy.com. I have a Dedicated Server with GoDaddy along with the Plesk Parallel Control Panel. Plesk is the manager for my site.

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.

You pretty much answered your own question. Plesk said files were missing, and depending on the context that would suggest that the updater was corrupt, or the upgrade process didn't work as expected and the resulting install is now corrupt.

This is a perfect example of why you use a development environment. If you have spare domains on your plesk licence then setup a duplicate of your site and do these sorts of upgrades there first.

What you need to do at the moment is to get the site running again on the original version. You should hopefully have a backup of the original working site, so restore from that.

Once you are up and running again, look into why it could have failed. Make sure the versions of PHP, MySQL etc are the correct version for the wordpress version you are moving to, and make sure that your plugins are supported on that version or wordpress too. If so, give it another go on the development site and see if it was a one off glitch (in my experience these are pretty common with plesk / cpanel etc). If it fails again maybe google some of the key phrases or error codes from the error message and see what others have done.