all day I tried to update several plugins using the automatic update function. I appears that wordpress has the problem every time that it cannot write the new plugin file to the folder "/wp-content/upgrade/". So this error occurs every time:
Warning: unlink(/wp-content/upgrade/some_plugin.zip) [function.unlink]: No such file or directory in /wp-admin/includes/class-wp-upgrader.php on line 146
Archive is not compatible PCLZIP_ERR_MISSING_FILE (-4) : Missing archive file '/wp-content/upgrade/some_plugin.zip'
Permissions of /wp-content/upgrade/ are set to 777.
When I manually upload the file "some_plugin.zip" to /wp-content/upgrade/ WordPress deletes the file and the same error occurs.
Would be nice if you could help me because I need to update the plugins for security reasons.