Hi Ally,
Here's something that might be a simpler solution. I saw a post where someone else was having the same problem = store content not installing. Ricalynn gave a suggestion of - Try making a factory reset folder and install some/all store content there to see if the items get installed and stay installed.
What a Great idea!! -- Thank you Ricalynn!!
Here's the link on how to do a factory reset.
Factory Reset: Fix Your Game with 1/4 the Time of a Reinstall
http://www.carls-sims-3-guide.com/forum/index.php/topic,7507.0.htmlI hope you find this a little simpler and will work for you
MrsFlynn