[MAC] Why am I having trouble downloading, installing, or launching Island Paradise on Mac?

Origin ID: Nessa1992
Are you opted into the Origin Beta? I don't know
OS X version: 10.8.4
Processor: 2.5 GHz Intel Core i5 ; Memory: 4 GB MHz DDR3 ; Graphics: Intel HD Graphics 4000 512 MB
Expansions you have/have active: Generations, Ambitions, Pets
Any error message received: Error 65538:15000
A detailed description of what is occurring: I purchased the University Life expansion pack (downloadable one) and when I click to download it I receive the 65538:15000 error message. 
A detailed description of any troubleshooting you have already attempted: I have uninstalled and reinstalled my Sims 3 game and the expansions, I have uninstalled and reinstalled origin, I have restarted my computer, I have logged out of origin and logged back in, nothing seems to work. 

Ursula: We added a workaround to the first post. Can you please try this?