I had 5 plugins with updates. After updating all of them through the Available Updates tool they disappeared from the Network Plugins page. I received errors like this for all plugins:
The plugin custom-post-type-ui/custom-post-type-ui.php has been deactivated due to an error: Plugin file does not exist.
The folders still exist in /wp-content/plugins/
When I deleted the folders and uploaded them through FTP they do not appear on the Plugins page. When I install them through wp-admin I receive this log text:
Downloading install package from http://downloads.wordpress.org/plugin/custom-post-type-ui.zip… Unpacking the package… Installing the plugin… Successfully installed the plugin Custom Post Type UI 0.7.1. Network Activate | Return to Plugin Installer
But when I click Network Activate, I receive this error:
The plugin does not have a valid header.
This happens for all 5 plugins and only happened beginning today.