Sometimes your EndNote library may become damaged or corrupted. This often occurs when your library has been saved on a cloud service or when the data folder has been deleted or moved. 

To recover a library:

1. Close your EndNote Library.
2. From the File menu, select Library > Recover Library.
3. Click OK.
4. Select the library (.enl file) you wish to recover.
5. Click Open > Save. Give your EndNote Library a new name. 
6. EndNote will display a dialogue box stating the number of records saved. Click OK.
7. From the File menu, select Open Library.
8. Be sure to use the copied library in place of the original damaged library.
9. Click Open - your recovered library should now be ready to use.

Tip: Further in-depth information on library recovery can be found here.