Moodle can’t add activities into class

[Solved]

YUI popuphelp-min.js is blocked by privoxy at generic path filter in default.action file (in your privoxy installation directory)

{+block{Path matches generic block pattern.} }
/(.*/)?((flash)?pop|live(cnt|count(er)?)).*\.(js|php|cgi)

Solution:

add your moodle domain in {-block} section after all {+block path generic block pattern} in default.action file in your privoxy installation directory.