I keep a back up copy of my endnote library on an external hard drive. When I opened my main library today, all the groups had disappeared and the references were all unfiled. The groups were still there when I opened the back up copy, however, when I tried to copy the back up onto the main computer the groups disappeared again. Does anyone have any idea how I can get them back?
Endnote libraries consist of two parts. The .enl file itself and the associated folders and files in the .DATA folder located in the same place as the .enl file. Sounds like you are only copying the .enl file itself.
To ensure that the appropriate groups and attached files are transferred, the best way to transfer a library, is to compress it, or send it, (depending on your version of Endnote) to create a (sometimes humongous) .enlx file, which the software can unpack in its new location. There have been discussion about using backup or synchronization software to assist in the transfer of the library and associated files more seamlessly, here in the forum.