Error message and loss of image in lr4 develp module

Question

Recently while working on files in Develop that I had previously made develop changes to suddenly there is a black dot in the upper corner of the image and an error message " there is an error with the image" or something like that.  The image is then immobilized, unable to make any further changes.  It is removed completely from every place I've copied it to. 
What's up? This is sort of frightening.
I work on i Mac OSX 10.6.8
I probably need more memory (4GB) and have just ordered more to have installed
I use back drives for my library and images store the main library on hard drive not the Mac hard drive.
There are about 10800 images in this library. 
I've been working with Lr since LR 2.5 or so
Help.

Answer 1

Pinotmom wrote:
Rob, yes, the images are DNG.
DNG has some check codes which are computed and stored (in the DNG file) when DNG is first created (and presumably not corrupt), thus if image becomes corrupt afterward, Lr should say so, in no uncertain terms, when going to edit in develop module (it recomputes check codes over critical data and compares them to originally computed values). UPDATE: That is probably what the "black dot" was on about.
Pinotmom wrote:
I'll have to check if I have auto-write on or off. I wasn't using it for a long time and then switiched it on.
Again, in case of DNG, since the static data (e.g. raw image) check codes are not recomputed when re-saving xmp, Lr should tell you if image was subsequently corrupted, whether due to writing xmp or otherwise. UPDATE: it probably did tell you that (the "black dot").
Pinotmom wrote:
Would you mind giving me an explanation of how you'd recommend making the backups?  and how to do it in the future?
I use Acronis True Image, but really any method will do, as long as it copies them from one drive to another physical drive. The only thing I recommend is:
* Make backups of original raws once (maybe more than one copy, but never overwritten).
* If proprietary raw, raws never need be backed up again, since they won't change. If DNG (or rgb), then one needs to either backup DNGs repeatedly (if you're an xmp saver), or just backup catalog (up-to-date settings and metadata are in catalog, but will be in xmp too, if up-to-date metadata has been saved).
Pinotmom wrote:
I'm ready to jump to Aperture....
Why come? (understand that Lr is not at fault here, and Aperture won't be any better at preventing corruption to your images due to hardware failure)
Pinotmom wrote:
how can I help rally for the option to prevent LR from writing/rewriting etc.
here is one way: vote and/or comment here - http://feedback.photoshop.com/photoshop_family/topics/add_an_option_to_prevent_writing_bac k_into_input_files
Pinotmom wrote:
thank you too.
You bet. - be sure to let us know what you find out, OK?
Rob