Thanks, but this is unfortunately not the problem I have, or I would have solved it within the first 10 minutes.
As you've discovered, re-importing photos will often lose metadata (edits, keywords, captions, collections, etc.), and thus re-importing is the last resort when you can't recover a working catalog.
In your case, I suspect the problem is that at some point Windows renamed drive letters. Rather than worry about how that happened, let's focus on getting a working catalog. You said your catalog backup references the F: drive, rather than the E: drive. That is easy to fix, using the methods described in the link that DJ_Paige posted above.
1. Once again, make a copy of the backup catalog and open LR on that copy.
2. In the LR Folders pane, find the F: drive. The folders listed under the F: drive should have a "?" on them, indicating they are "missing" (that is, the locations that LR thinks they are at do not actually exist).
3. Right-click one of the top-level folders and select Show Parent Folder:
Repeat until the topmost folder is F:.
4. Right-click the topmost folder F: (which will have a "?" on it) and select Find Missing Folder:
A file browser will open -- select E: and click Select Folder.
5. At this point, the Folders pane should show the E: drive, with no "?" on the folders, and you should be able to navigate to all of its folders and display the pics in the folders. The Folders pane may still show the F: drive, with "?" on its folders -- if so, restart LR and it will disappear.
Thanks John! will try that in the morning. Sounds plausible for the backup catalog. But could there possibly be a way to actually recover the original, latest catalog? Or must I consider that lost after the "failed" re-importing?
You could try the same method on the original catalog, but it's not clear from your description how many changes were made to it. You can try both (the original, the copy of the backup) and see which one is better.
John, thanks a lot! Everything worked exactly like you described, and the backup catalog is working perfectly now. I'm a happy camper :-) Well, except for still losing a lot of recent work, but that'll teach me...
This recovery method does not work on the original catalog, however, since that one does not point to a fictitious HD and the problem there is different. I'm not sure if all the data are really lost for good from that catalog, though, since the file size is still bigger than the previous backup. Wondering if there's still a trick to recover that original catalog too?
Thanks again for everybody's input!
You can recover the individual edits and metadata changes (caption, keywords, etc.) to photos in the original catalog: Select all the photos you've worked on in that catalog and do Metadata > Save Metadata To File. Then in your correctly working catalog, either import those photos (if they're not already in the catalog) or select the photos and do Metadata > Read Metadata From File. This won't recover changes to collections, stacking, books, or other kinds of changes.
that, unfortunately, does not work. Since the keywords, ratings (and edits) are missing in the original catalog, all this method does is also delete them in the working backup catalog without bringing the edits back. I've tried it with 2 photos where I'm lucky enough to have a .jpg copy of what was the final edit.
Wow, John you were right the first time! I had forgotten about the greyed out F: drive that still showed up in the folders of the original catalog. So, after deleting the re-imported E: drive again, I was able to apply your method to the F: drive there. I recovered the complete latest version of my catalog from before the crash.
Thank you so much!