Plugins have disappeared & "this plugin does not have a valid header" on all

URGENT… AHHHH PLEASE, PLEASE help somebody. All my websites were working fine – now all of a sudden I am getting the error messge “this plugin does not have a valid header” on ALL plugins – I’ve tried installing all sorts – so it’s not local to individual plugins.

I have trawlled the internet to find a solution and most solutions seems to involve deleting the plugins via FTP and then manually re-installing. I have tried this – but to no avail. Also, when I click on my plugins in the sites – no plugins are showing even though they are installed (manually or automatically – it’s the same).

I have also tried the other solution suggested which was to change the “tested until version ….” in the readme file to a later version than the wordpress I’m using. That did nothing. And some of the plugins don’t even have readme files.

But either way, I shouldnn’t have to be manually fixing this on EVERY plugin.

I thought it was something to do with the latest version of WordPress but the same thing is happening in my older websites and plugins that were working are now not working.

I don’t think it’s a browser issue because I get the same problem on my ipad using Safari as I do with Windows Google Crome.

PLEASE HELP – I have websites to finish this weekend.