You can change the permissions for the disk by using nautilus as root. To do
this use gksu or just sudo to launch nautilus from a terminal. After giving
your password then wait for nautilus to open. If you are not in GNOME use
nautilus --no-dektop or you may lose your access to the desktop of XFCE or
KDE. You can use any file manager if you don't want to use nautilus.

In nautilus go to the folder or partition where you are saving and right
click and choose Properties. Then click on the permissions tab. Change the
owner from root to you and make sure it says read write access. Check the
box to change files in subdirectories. Click ok or apply and then re-try
after it is done.

You can also do this from the commandline,but I find navigating from the
commandline harder. You use chown, but type man chown to find the syntax. I
forget it and need reminders. I blame old age and lack of practice.

If you still cannot save then you may have to create a folder as root and
then change the permissions for it as a workaround.