Uploading media installed in MAMP

Hi, I’m a new user trying out Omeka S at home running on MAMP (while I wait for it to be installed at my university). I got it going and created some pages but when I try to upload Media from my hard drive I get “Omeka S encountered an error”. That’s it. Same if I try to use a YouTube link. Any advice welcome. I had none of these problems using the Sandbox.

See Omeka documentation : https://omeka.org/s/docs/user-manual/install/#install-on-windows-or-mac-os-basic-development-purpose-only

Thanks, I’m running on our university server now!