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.

I rebooted for something else and it took care of it.
I have my /mail on /data too so everything was screwing up.
Its all good now. Not sure why that happened.

It's unfortunate that the problem didn't happen to reappear because that
sort of thing reinforces the bad old microsoft troubleshooting methods
(#1 - reboot, reboot, reboot or, if #1 doesn't work, #2 - reinstall).

Generally speaking, if something doesn't work in linux, you can find
what's misconfigured and fix it - rebooting generally doesn't work,
though it can be a lazy man's way of running the system startup commands
without having to do anything, or even to know what sort of things
happen on startup.

Too bad we didn't get to find out what your problem was. Sounds like you
tweaked something on that external disk, and in the process, cleared up
the permissions/ownership issues.

Since I built my this pc over a year ago, /data has been just fine. No
idea what in the world happened and as I said, restarted for a different
reason but - was really surprised it fixed it.

I was looking through the logs but Ive no idea what Im looking for.

Well, you might want to save the file in your home directory instead of
the partition where you apparently don't have write access.

If you were expecting that partition to be writable by you, then you'll
want to find out what's wrong. Have you ever written to that particular
partition from that computer before?

How did you mount the disk? manually or automatically? what is the
filesystem type? For further support, please do a long listing of the
/data partition which will show the ownerships and permissions, and
everything should become clear at that point.