Today I realized that I cannot execute successfully 'org-mobile-push'. In particular here is the output from '*Messages*':

Creating agendas...
Agenda written to Org file /Users/drorata/Dropbox/MobileOrg/agendas.org
Creating agendas...done
Saving all Org-mode buffers...
(No files need saving)
Saving all Org-mode buffers... done
Copying files...
Writing index file...
org-mobile-create-index-file: Wrong type argument: sequencep, :grouptags

I first step I took was to update the package; now 'org-version' yields 
"Org-mode version 8.2.4 (8.2.4-3-g7fe99a-elpa @ /Users/user/.emacs.d/elpa/org-plus-contrib-20131209/)". However, problem is still here.

Next I don't really know what to do... I have all my emacs' settings in 
https://github.com/drorata/emacs_setup

How can I debug this problem and solve it?