I am also having this problem. I've been getting "An unknown error has ocurred in Outlook" when I try to receive mail. Error code 150. Sending mail works, ironically. After completely deleting and re-installing (thinking it was an Outlook problem), I still have the problem. Outlook is not broken - I added my gmail account, and it works just fine.
Clearly Cox did something on December 5 that broke POP email retrieval using Outlook 2011 for Mac. It's Sunday today - tech support closed. Will call them tomorrow.
Anybody have any luck fixing this yet?
A little more research - Outlook 2011 uses SSL v2. Note from tech (KevinM2) below says Cox changed to requiring SSL more recent than v3. But he says they changed back in April. Doesn't really explain why this problem started for all of us on Dec 5 ... if what KevinM2 says is accurate, it should have stopped working in April.