"An unexpected error occurred": Can't search/upload themes

Hello,

I’m really not very technical, so I’ve no idea what’s happening here. I’ve got www.remarpro.com on five of my websites and I can’t search/upload/add new themes on any of them all of a sudden.

It says this:

“An unexpected error occurred. Something may be wrong with www.remarpro.com or this server’s configuration. If you continue to have problems, please try the support forums.”

I have tried updating to 4.2.3 to see if this solves and it doesn’t. I’ve disabled and re-enabled plugins, which also did nothing. I deleted plugins on one site and re-installed and nothing. (Anecdotally, it seems to have occurred since the 4.2.3 update was available.)

I read somewhere it’s about wp-config.php, but daren’t change as I’ve no idea what to change/how to change to and if that’s the issue?

I also read it could be a hack forcing CRON jobs or something, but there’s none of that going on.

I also deleted wordpress completely and re-installed on one site and nothing.

rowenajayne.co.uk
electricdomestic.co.uk
sciencehappy.co.uk

Please help?