The problem was a corrupted let-plist package in my elpa folder. After reinstalling the package all works fine. Johannes Am 03.04.2017 um 20:05 schrieb John Kitchin >: That looks like an issue with helm-Bibtex. You might try updating it and/or raise an issue with that package. On Mon, Apr 3, 2017 at 11:03 AM Johannes Brauer > wrote: that’s what I get executing (require 'org-ref): Debugger entered--Lisp error: (error "Required feature ‘let-alist’ was not provided") require(let-alist) byte-code("\300\301!\210\300\302!\210\300\303!\210\300\304!\210\300\305!\210\300\306!\210\300\307!\210\300\310!\210\300\311!\207" [require bibtex browse-url hl-line ido json url-queue dash let-alist seq] 2) require(biblio-core) byte-code("\300\301!\210\300\302!\210\300\303!\210\300\304!\210\300\305!\210\300\306!\210\300\307!\210\300\310!\210\311\312!\207" [require biblio-core biblio-doi biblio-arxiv biblio-crossref biblio-dblp biblio-hal biblio-dissemin biblio-download provide biblio] 2) require(biblio) eval-buffer(# nil "/Users/johannes/Library/Preferences/Aquamacs Emacs/Packages/elpa/helm-bibtex-20170321.1306/bibtex-completion.el" nil t) ; Reading at buffer position 1340 load-with-code-conversion("/Users/johannes/Library/Preferences/Aquamacs Emacs/Packages/elpa/helm-bibtex-20170321.1306/bibtex-completion.el" "/Users/johannes/Library/Preferences/Aquamacs Emacs/Packages/elpa/helm-bibtex-20170321.1306/bibtex-completion.el" nil t) require(bibtex-completion) byte-code("\306\307!\210\306\310!\210\306\311!\210\306\312!\210\313 \314\211 \314 :\203f -- John ----------------------------------- Professor John Kitchin Doherty Hall A207F Department of Chemical Engineering Carnegie Mellon University Pittsburgh, PA 15213 412-268-7803 @johnkitchin http://kitchingroup.cheme.cmu.edu