I had problem in my ubuntu 14.04 that I could not send or receive any messages if I am part of a group chat.
can not start group chat, can not send message in group chat.
it shows yellow icon (message stuck)
But I could send receive message in 1-1 chat without problem
How to solve:
signout from skype and to make sure its not running
killall -9 skype
in your terminal go to your home directory
mv .Skype Skype.backup
now start skype again it will ask for username password etc just add them
skype will start, and start loading all history. give it some time and wait until its done.