This is about the 4th time this has happened to me within 2 weeks and I'm really starting to get annoyed with Skype. Basically I can't join the call that all of my friends and I are always in and I can't receive messages or send messages from them. I don't know how to fix it but I really want to.
Before trying to isolate an issue, it's always best that one is running the latest Skype release. Which may in itself resolve the issue.
A new version has just been released August 02, 2011:
Please click the "Get Skype" link at the top of this page and download the normal version of Skype, NOT the beta version to get this new version.
This new version is 220.127.116.11 to check what version you have, using the main Skype client window please do:
Help -> About Skype
Make sure you and all other group call participants are using the latest Skype version.
You can try with the latest 6.7 version of Skype that you can download here