Quit using Mendeley people!

They started encrypting your database so you cannot easily move it over to other tools any more.

See:
https://www.zotero.org/support/kb/mendeley_import

That link also helps you saving your data before it's too late.

(Elsevier are a bunch of crooks, blocking interoperability one-way and not the other. Almost as bad as Google blocking uBlock for your safety...)