WordPress problem with FTP

I’m currently having a problem with my FTP server with WordPress, it’s been working fine since I got, but about two days ago or so it’s been acting up.
It says this whenever I try to install a plugin, or somewhat similar…
Downloading update from http://downloads.wordpress.org/plugin/meenews.zip.

Unpacking the update.

Could not copy file /public_html/blog/wp-content/upgrade/meenews/meenews/js/ui.core.js

It’s says that for just about everything I do, not the last part exactly, but it always seems to say Could not copy file.
It’s really starting to get on my nerves.

I run on WP 2.81, and can’t update to 2.82, because of the same problem.
Please tell me whats going on!