Milton Fitzgerald's Reload Missing Xrefs (PDF) outlines the steps for reloading missing xrefs in an AutoCAD drawing. Download the full procedure or follow this condensed version of the steps:
1. Open the existing layout (the drawing will probably be in Paper Space / Layout; Layout1, is the default).
2. Locate the file or folders with the xrefs via the External Reference dialog box (under the Insert tab).
3. Select the files under Found at and reload into the drawing. Click the ellipses (the three dots at the end) and browse to the proper file location. Click Open.
4. For adding xrefs, use the Bind dialog box. Select Bind if you just need to view the drawing, or Insert to permanently attach drawing to the file.
5. Your updated file should now look correct.
6. If you are still missing files, you will be able to see which ones in the dialog box. You will have to ask the person who sent you these files to resubmit them, then go through this process again to reload the missing files.
NOTES FROM CADALYST TIP PATROL:
Sometimes folders change names or outside sources send a file that references other files. Sometimes those files are missing or they are just in a different folder than the one the reference link remembers. This happens. Thanks, Milton!
Follow-Up: Reload Missing Xrefs
The processing of finding missing xrefs is a subject near and dear to our readers' hearts. Hugh Thomson and Chris Wade reminded us about the Reference Manager, which allows the user to select multiple drawings and see what xrefs are missing as well as their saved paths. Users can quickly reselect the correct location of the missing xrefs and apply the changes to the parent drawings without having to open them, a handy way to quickly check drawings from a third party. Reference Manager is located on the Start Menu with your AutoCAD program. Note that if your AutoCAD version is newer than the files, the files will be upgraded to the current version. If this is problematic, it can be corrected by using the free Autodesk TrueView program from the Autodesk Web site to convert them to any other version.
On a related note, Shawn Evjen wrote to remind us that some xrefs may contain a lower-level xref that has been set to overlay instead of attach. In this case, it will not show up in a drawing when expected. To change the type of xref from overlay to attach, open the file that contains the overlaid xref. Then in AutoCAD 2000-2008, open the Xref Manager (Insert / Xref Manager), select the name of the xref, and double click the word Overlay to change it to Attach. In AutoCAD 2009 you can find the Xref Manager under Insert / External Reference.
Ronald Maneja offered yet another way to reload missing xrefs: "Copy all the xrefs to the same folder where your final drawing is located. When you open the final drawing, all the xrefs will be automatically loaded, and you do not have to do it one by one. By default, when an xref is not found, AutoCAD searches the xrefed drawing in the same folder where it is located.
"If all your xrefs are in a separate folder and you do not want to mix the final drawings with the xrefed drawings, another workaround is to add the directory of the xref folder to the support path of AutoCAD. Once a final drawing is opened and AutoCAD has found that an xref is missing, then it will also search the supported paths."
Finally, our own Cadalyst Tip Patrol member Kevin Sawyer shared AutoCAD's built-in method for finding errant xrefs and images, which hinges on the PROJECTNAME system variable. "This variable is stored in the drawing, so it can be set to values to suit each individual drawing on the same project. Go to Options / Files Tab / Project Files Search Path and Add a new entry. Give this entry a definitive name, maybe the name of the supplier of the missing xrefs or your own project number. Next, expand the branch just created, highlight the Empty and browse to a folder where the missing xrefs reside. You can create as many entries as you like as these are saved in your registry. Now when you open a drawing where the xrefs are missing, as long as you have carried out the procedures above, you only need to change the system variable PROJECTNAME to the name of the corresponding entry as entered. Any missing xrefs in that folder can then be reloaded. If they are not found in that folder, AutoCAD then searches the support file search path in the usual fashion."