There may be issue related to whether both parties are working across platforms and if they are using different versions of EndNote. Are both using Windows (what versions), or is one using Windows and the other using a Mac? Also what version of EndNote is each person running?
If both parties are working across platforms, here’s some info from the EndNote Knowledge Base for transferring files:
EndNote: Transferring Windows EndNote libraries to a Macintosh (and vice-versa)
EndNote Libraries that are created on the Mac version of EndNote 8 or later or the PC version of EndNote 8 or later are compatible across platforms; they can even be shared over a mixed-platform network. With the database structure of EndNote 8 , your libraries will not be backwardly compatible with older versions of EndNote. Version 8 and later databases are compatible with the EndNote 8 and later programs only. For more information on the EndNote 8 and later Library format, go here.
To share a library, use the following steps.
If all users are using EndNote X and later:
You can save your complete library (the EndNote library.enl file as well as its associated .DATA folder and all of its contents) to a single compressed .enlx file in order to easily transfer your library. Note: This compressed library may only be opened with EndNote X or later.
- Open the library in EndNote.
Endnote X/X1 : From the “File” menu, select “Send to” and then “Compressed Library.” Endnote X2 and later : From the “File” menu, select “Compressed library (.enlx)” and then “Create…”
- Use the file dialog to save to an EndNote Compressed Library (filename.enlx).
To restore a compressed library file:
- Use EndNote X or later to open the filename.enlx file, which will extract the .ENL file and the .DATA folder to the same folder where the .ENLX file is located.
- Use EndNote to open the filename.enl file as you normally would to use the library.
If all users are using EndNote 8 and later :
If you plan to email an EndNote 8 or later library to someone, you must send all of the files found in your library’s DATA folder. While you cannot attach an entire folder to an email, you can use a third party program (such as WinZip or StuffIt, or Windows Compressed folders) that can zip your library and DATA folder into a single file to send via email.
Windows to Macintosh for EndNote 7 and earlier :
- If you are on a network you can simply copy the library from the PC to the Macintosh. If the machines are not networked you can transfer the files via portable media (CD, floppy, zip disk, USB key drive, etc.) or you can email the file(s) to yourself.
- In the EndNote program on the Macintosh, choose Open from the File menu and select Open Library. As long as the library has the .enl extension, EndNote will display it.
Macintosh to Windows for EndNote 7 and earlier:
Any library created by the Mac version of EndNote (prior to version 8) can be used by EndNote for Windows. Version 8 and later databases are compatible with the EndNote 8 and later programs only. No conversion is necessary, however you should change the name of the library to include the .enl extension (for example, Medicine.enl).
- If you are on a network you can simply copy the library from the Mac to the PC. If the machines are not networked you can transfer the files via portable media (CD, floppy, zip disk, USB key drive, etc.) or you can email the file(s) to yourself.
- Start the EndNote program in Windows. (If you see a dialog prompting you for a reference library file, choose Cancel.)
- Select Open from the File menu, and choose Open Library. Under “Look in” navigate to the location of the library you want to open. If your library does not have the extension .enl or .lib it will not appear in the dialog. If that is the case, select All Files *.* from the file type list at the bottom of the dialog and you should be able to see your library.