Sony VAIO VGN-Z51WG skype problem

Hi, I have a Sony VAIO VGN-Z51WG, when it goes in to sleep mode, and then I wake it up, there is a problem with Skype.

I'm logged in to Skype but all my contacts see me as offline.

If I reset the laptop Skype works fine, it's only when it come's back on from sleep mode that I have the problem.

Any ideas?

Thanks.