This is very annoying.
When trying tu run a system upgrade, i get this message.
We're sorry, no components are available because you cloned the Magento 2 GitHub repository. You must manually update components as discussed in the Installation Guide.
I uninstalled Magento , and installed it again.
I did not clone anything.
Which installation method are you using for Magento?
I figured it out.
When transferring all magento uncompressed files by FTP to my server, there was an error, saying that one or more files already were on server. Then I clicked on overwrite.
So, in my magento 2 installation there was a missing file, that caused this error.
this time, i transferred not all files in one operation, and this error did not come up.
So the installation is eventually working.