Even though Lightroom now uses the Folder
paradigm rather than Shoots (as was the case during the
public beta), it doesn't display the full disk/folder hierarchy in the
tree form that most users would be familiar with. This means that
moving folders from disk to disk or even to a section of the hard disk
not shown on the Lightroom Folders panel very often needs to be
done using OS level tools such as Drag/Drop or even the Move
command. The problem with this approach is that Lightroom can easily
lose track of your files, and this results in the ? symbol being
displayed.
Note: The screenshots used below are based on
Adobe Lightroom V1.1 for the Mac but should be very similar in
appearance to the Windows version. Nevertheless, I will identify
those areas where the Windows version differs either in appearance or
functionality.
Clicking the ? symbol will cause a small
navigational dialog (Figure 1) to appear. This dialog will provide
information as to where the file was originally located along with an
option to find (Locate) it again.

Figure 1
When the files displaying the ? symbol all lie
within the same folder then it's probably reasonable to use the above
method to find them, especially since Lightroom will automatically
re-establish the link with any other missing files within that folder.
However, as you'll quickly realise, clicking the ? symbol is
slow and laborious for finding files when multiple folders have been
relocated or disconnected. There must be a better wayÖ
There is! Look at the Folders panel (left side of Library
module) and you should find that the folder/subfolder containing the
files that Lightroom can no longer find are shown in
red text (Figure 2). It is the red
text that Lightroom uses to help you identify a folder/subfolder that
contains files that it has lost track off.

Figure 2 - Missing Files and Folders
On the screenshot shown above I have highlighted the
missing subfolder in yellow and also shown how the Library panel
also displays the problem. In this example I have a subfolder
containing 110 files that Lightroom can no longer find, which means
they cannot be edited in the Develop module. Finding these files
is relatively straight forward, but I should also point out that there
may be a perfectly good reasons why they are being flagged as missing.
For example, they are stored off-line on a portable disk drive,
file-server or a DVD. Typically, when such devices are reconnected
Lightroom will automatically find the files and the ?
symbol will disappear.
Tip: - Lightroom may well take a few
minutes to find files and folders when a connection to an off-line
disk drive or file-server is re-established. In such cases, Lightroom
will probably scan the entire folder hierarchy of the disk drive/
server. Fortunately, this only occurs on rare occasions such as a
server storing 10's of thousands of files. Ideally, you should plan
to have this type of device connected before launching Lightroom.
[Authors note - the Lightroom Library or Catalog (as it's
called in version 1.1) folder should not be placed on a file-server.]

Figure 3
On the Mac you should Control-click (right-click
when using two button mouse) the folder/subfolder, a pop-up menu will
appear (Figure 3). From the pop-up menu choose the command Locate
Missing Folder, a dialog should appear (Figure 4 below).

Figure 4 - Locate Missing Folder Dialog (Mac)
The dialog shown in Figure 4 above gives you access to
every hard disk connected to your computer or CD/DVDs if they're in the
tray. Use this dialog to navigate to the location where the folder is
now located, then select this folder (not the files). Finally, press
the Choose button and allow Lightroom to do its stuff.
The method described above also applies to the PC version although the
dialog is called Browse for Folder and the Choose button is
replaced by OK (shown as Figure 5 for information).

Figure 5 - Browse for Folder (Windows XP/Vista)
Figure 6 below shows the final result of the steps
described above. Note that the folder that was originally shown red and
located with the Render Tiff and PSD Photo Library is no longer red,
the associated thumbnails no longer show the ? symbol and the
Missing Files item is gone from the Library panel.

Figure 6 - All's well again...
This example has concentrated on a single missing
subfolder. However, if you are dealing with a situation where
multiple subfolders are missing, then use the Locate Missing
Folder/Browse for Folder dialog to navigate to the top level folder
(i.e. DNG Photo Library in Figure 7). Select the folder and click
Choose/OK. Lightroom will re-establish the link to all of the nested
subfolders.

Figure 7 - Multiple Missing Folders
Tip: - If at the end of this exercise you
still have thumbnails that show the ? symbol it's probably
because the original files have been deleted from your hard disk.
Again, doing so using the OS commands means that Lightroom has no way
of knowing that the file was deleted. If this is the case then simply
select all of the offending files then choose Delete Photos
from the Library>Photo menu.
You can avoid getting into a situation where Lightroom
loses track of moved folders/subfolders by using a variation of
above. Actually, it's a hidden feature. Basically, you "push"
the folders/subfolders from their original location using OS tools such
Drag/Drop, Copy/Paste or Move commands to their new location (eg a
second internal disk, portable disk drive or DVD). Then from the
Lightroom Folders panel press Control+Option-click (Mac)
or Ctrl+right-click (PC) to expose the additional folder action
command Locate Missing Folders (remember that this command is
normally only available when you have missing files/folders) - see
Figure 8 below.

Figure 8
The Missing Folder/Browse Folder dialog (exactly
the same dialog as shown in 4/5) will appear, and the steps described
above can again be used to select the folder in its new location. Once
satisfied that Lightroom is now referencing the files/folders in their
new location you can delete the files from their original
location.