I had a look at my external HDD with Gparted and I noticed that one of it's partition was corrupted (a previous failed installation). So I formated it and now the installer does not hang anymore.
I let this bug open because Ubiquity is not suppose to hang in such a case. ** Summary changed: - Unable to install on an external HDD + Unable to install when a partition is corrupted on disk -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/727351 Title: Unable to install when a partition is corrupted on disk -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs