If your EndNote library is corrupted or missing a file (.enl) and you do not have it backed up to EndNote Online, there are a couple of solutions.
The recommendation is to sync your EndNote library to your EndNote Online account.
Recovering EndNote Library with .data file
To work properly, EndNote Libraries have two files: .enl and .data
The .enl file (purple icon) is used when you open and work in an EndNote library. The .data folder/file helps your EndNote library run properly. These two files must always be saved together (ex: in your Documents folder on your computer).
If your .enl file was deleated, or not moved to a new computer, you can recover your EndNote library with the .data file.
These instructions only work if you are using EndNote x8, x9, EN20 or EN21. This will not work with x7 and older.
Open a new Notepad document. Leave the document blank
Choose File > Save As...
Save the document in the same location as the Data folder. Give the file, the same name as the Data folder and adjust the suffix to .enl (For example, My EndNote Library.txt will become My EndNote Library.enl)
Click on Save
Your file will convert to a .enl file and should include the references from the deleted/ missing EndNote Library