Cannot Update or Install Plugins Through WP Dashboard

I’m unable to update or install plugins through the WP dashboard.

When updating a plugin, it runs through downloading the new version, removing old version, updating to new version, re-activating plugin. But when I go back to the plugin page it actually has not been updated. No error message is displayed.

When installing a plugin, it downloads the plugin and supposedly installs it with no problem. When I click on Activate plugin I get the error “The plugin does not have a valid header.” When I check the server, the plugin folder is not present.

I can update and install plugins with no problems using FTP directly.

This site is installed on a VPS that I manage. I have other WP sites installed that do not have this issue.

Any suggestions?