If you open your catalog and find that there are grey boxes instead of thumbnail images, and/or [ ! ] in the upper right corner for each image - don't panic, Lightroom just wants to know where your images are located. Fixing this issue is just a couple of clicks and you're good to go!
In the Library Module
1. Click on the [ ! ] symbol in the upper right corner of any image
2. A dialog box will pop up. Click on "Locate" to proceed.
3. Locate this specific image's file. Make sure "Find nearby missing photos" is checked, to re-associate all other files! Then, click "Select."
4. Lightroom will locate the image files(it may need a moment), and the [ ! ] icon will disappear.
Error message: "This file has already been associated with another file in the catalog"
Most likely, you have successfully re-associated this image to this Catalog. Try closing Lightroom completely, and re-opening it. It may just need a quick re-start to fully update! :)
This error message can also pop up if you are a Master Catalog user, and have "cycled through" your file names. We recommend renaming the older file(s), then proceeding to re-associate the newer files as usual.
I've followed all of these steps perfectly, but Lightroom hasn't made any change!
Lightroom may be struggling to display the updates that it has made. Try closing Lightroom completely, and re-opening it.
I've followed all of these steps perfectly, and now the [ ! ] has been replaced with [ ... ]. What is going on?
The [...] symbol is Lightroom's way of showing that it is still "thinking." Once that symbol disappears, you may see your image update with any new changes(for example, ShootDotEdit adjustments).