Whenever I attempt to install a new plugin, whether it is via WP admin or by uploading via ftp, I experience the same problem(s) with ANY pluging I attempt to use:
1. First attempt of new plugin via WP: It downloads, unpacks and installs (according to WP Admin) . I then click on 'activate' and get "The plugin does not have a valid header". If I then look for the plugin in WP it is not there, although the folder is there on the ftp.
2. Second attempt of plugin via WP: Same as above but after the unpacking step it fails with 'Destination folder already exists'.
3. Manual install: If I upload the folder to the correct location it just does not show up in WP.
The fact that this happens with all plugins would suggest to me that:
a. possible problem with WP 3.5 and 3.5.1
b. web hosting issue
Has anyone out there got any advice here please? I am at my wits end!