This is the DLP forum so I will move this discussion, but I think the first point is - Skype does not use SSL - it uses a proprietary protocol.
Skype is trying to send NON-SSL traffic over the SSL port - the gateway is saying "this is NOT SSL so go away".
You need to set things up so Skype does not try to hide itself over the SSL ports.
this may help.
Otherwise, call your platinum support person.