Workling + Memcache error

Try to setup Echowaves, got the message error.

uninitialized constant MemCache

A workaround solution is
Goto vendor/plugins/workling/lib/workling/clients/memcache_queue_client.rb
add require 'memcache'

Just don't know why the error occur, it's basic. I tried to get the latest workling plugin. But no help.
!!!!
Anyway, add require 'memcache'. It works.