No acces to media library and upload error, but the file gets uploaded

I’m running the 3.5.1 version of WP.

And the website is running a few months perfectly fine, but yesterday it failed to upload some files. I opened this thread because I could not find the solution in other similar problems.

When I want to use a jpg or png file in a blogpost I just click add media.
The media library / upload screen pops up and the media library is not showing any files. But it has a lot of files in it.

Then, when I try to upload a file it says Error occurred when uploading. Please try again later.

So that didn’t work properly, but the strange thing is. When I click the media tab on the wp menu the file is uploaded correctly but I can’t access it from my blogpost page.

So it is not an upload problem, but a media library problem.

I already tried it with all plugins deactivated, and with a few other themes. The wp-content folder chmod is set to 755 and nothing made any difference…

That is what makes it complicated to search for similar problems….

I hope someone has a solution for this mindcrackin’ problem…

Thanks!