Following your instructions, here is what happened.
- I opened JabRef and made a small change of some entry.
- I l clicked the save button and saved successfully, and meanwhile the lock file was generated and stayed here after.
- Then I made another change, but was unable to save.
- I deleted the lock file and then saved successfully.
Then I did another experiment and found something interesting. The bib file is in a Dropbox folder, so I thought maybe the Dropbox was trying to sync the lock file while Jabref was trying to delete it and wasn’t able to do so as as a result. So I moved the bib file outside the Dropbox, and guess what? The problem disappears. Not only that. There was no lock file generated, unlike before. This is rather odd because the bib file has always been in the same Dropbox folder and there had been no problem until a while ago. I would also like to keep putting it in the Dropbox folder so I can access it anywhere I want. Any ideas?