I'm using wp 3.4.2 on a hosting service. I can access the ftp server and make changes using a ftp client (ie I have the correct credentials). I inherited the website and I'm trying to update everything, but as a precaution I started with the plugins.
The problem
When I try to update a plugin using the admin dashboard, after clicking "update now", the page keeps loading for several (about/at least 5) minutes. Afterwards I get a Error 503 Service Unavailable error. FTP settings are hardcoded in wp-config.php. This happens with all the plugins.
I solved it already, answer below.