This has most likely to do with how your system is setup.
http://codex.ww.wp.xz.cn/Common_WordPress_Errors
Probably directory and file access settings:
http://codex.ww.wp.xz.cn/Changing_File_Permissions
If it’s not possible to get this going for you, you could try contacting your web hoster.
Is there a list of what all the default permissions are supposed to be set to?
A very simple requirement list:
https://ww.wp.xz.cn/about/requirements/
Your problem could be related to security settings (e.g. FTP access is a different user than the Apache user), or your disk usage could be 100% — dunno, but ask the company that hosts your site.
