I was having the same problem. Ubuntu 14,04 here. I found this answer in a forum that solved the problem for me.
After struggling a bit, I found some useful commands. You can type these in any skype chat window.
/dumpmsnp
- show details about your connection
/showplaces
- show where you are currently connected
What was happening was that /dumpmsnp command was showing "LoggedOut", but I was online and talking almost normally (except group chats).
System: MSNP: Connection Data:
* Status: LoggedOut
To solve this "LoggedOut" issue, try this on any chat window:
/msnp24
and restart your Skype.
After restarting, /dumpmsnp output shows the following status:
System: MSNP: Connection Data (MSNP24):
* Status: LoggedIn
I don't know exactly why, but the /msnp24 command kinds of converted my account to this protocol and now everything works perfectly.