Edit rsgallery2.xml in the nightly build package com_rsgallery2._svn_rev_69.zip
Replace all
lib/rsgcomments/emoticons/
with
lib/rsgcomments/emoticons/default/
If you have previously installed this nightly build package with problem, you have to delete /components/com_rsgallery2 and /administrator/components/com_rsgallery2 manually, fix the rsgallery2.xml as above, and reinstall the component.