Actually I had a couple of problems both with the attachment system (which I remember) and with the Gallery.
In the attachment system I could manage to attach the file but not to refer it inside the post, as I was used to do – the related button does nothing. Plus if I try to see the preview and then the editing again, an error message appears next to the image warning of the failed upload.
In the gallery I have a ungodly amount of time to wait after pressing the upoload button, only to get a standard HTTP error message as a result (something about the size of packets, I can’t remember well). I am sure that the file size is under the limits.
I was about to post in the relevant section, but I postponed it to a second time… when I could log exactly the passages that cause me the errors.