If you are using Gigatribe version 3.06 and one of your contacts has installed the beta version (3.08.045), an incompatibility will prevent version 3.06 users from connecting.
Recommended solution: Uninstall version 3.06 and install the latest stable release, 3.08.038.
If you want to keep version 3.06.015 because your operating system is too old to install a 3.08 version, please note that beta version 3.08.045 has been removed. A new beta version is currently being prepared and will be compatible with 3.06.015.