Fixture library has "Lock" icon over it.

Hi all,
Anyone know what it means when a fixture library file has a lock icon over its normal icon when viewed in the file browser window?
Also, I can't delete the file with the lock icon like I normally would using a mouse right click and delete. It doesn't seem to make any difference whether or not I'm using fixtures from the library. Also, I did a full OS upgrade to the latest OS last night and hat didn't change anything. Now, of course I was working with a backup of the showfile so I'm not all that surprised the icon was still there. The only thing I haven't tried is manually rebuilding the show from scratch. It;s just the base rep plot for my theater, so recreating it wouldn't be a huge deal, but I'd rather not waste a day or two on it if I don't absolutely have to.
Thanks in advance.
-Mark

P.S. In case it matters (which I doubt, but...) the library in question here is the latest... Version 4.22.45.  Thanks!