LaCie external HD suddenly not mounting

I have a new-ish Mac Mini and a MacBook Pro. I've been slowly migrating my Pro files to the Mini for some flexibility/stability. I've had the LaCie HD hooked up to the Pro FOR EVER. It's only ever been on a Mac--never a PC.

The LaCie seems to be fine.

However, on the Mini, it's suddenly mounting (both partitions--don't ask, I made them long ago and can't recall why) with a little lock at the bottom left of the icon. When I Get Info and look at permissions I have to unlock it and all/any users listed are noted with "Custom" preferences.

I can't R/W--I get "The folder "Stuff" could not be opened because you do not have sufficient access privileges.

I've gone to Terminal, listed the volumes and tried to reset the nouchg--didn't help.

ANY ideas? I haven't retried it on the MacBook Pro yet. Honestly, I'm unnerved. I've been having a number of permissions problems lately on the Mini and don't want them migrating to the Pro...which sounds lame, but there it is...