Cannot upload *any* files

Hi
I’m investigating a client’s issue whereby they used to be able to upload to BuddyDrive via the front end but now get a message saying: “File is empty. Please upload something more substantial. This error could also be caused by uploads being disabled in your php.ini or by post_max_size being defined as smaller than upload_max_filesize in php.ini.”

I checked file upload maximum settings and also confirmed that they can upload via other means into the Media Library. Searching on the error it mostly comes from WP core files.

Anyone got any ideas about this please?

Thanks

Dan