Had this once with the current version, 5.3.011.
I think that they already know about this issue and working to solve it.
I thought it's something with the firewall but it doesn't looks like.
My solution that worked for me, founded among many forums is:
Start -> Run -> write '%appdata%\Skype' in this directory, delete a file named 'shared.xml'
But i know it doesn't solve the problem for all cases, meaning you may have like me windows 7 64bit, do the same solution but it won't work, why ? Don't really know.