Unknown Error Occurred when attempting to download Custom Content on my Sims 3 Game!!

If it's happening with only the launcher open, then that error is probably the result of having installed bad custom content.  Does it happen when you try to click the "Installed Content" tab? 

No I have a Mac and it happens when I go on my downloads file and try and click on the custom content to download it onto the game. The Launcher then opens and it then opens another page like it does when everything works but after a few seconds its comes up with 'unknown error occurred'.

It used to work fine. Do you think its the new custom content i am trying to download that is bad? Because the custom content i already have works fine in the game.

Yep, I definitely think it's the new custom content you added or maybe outdated mods.  I also have a Mac so I'm very familiar with unknown error and exception raised stuff.  The only times it happens at launcher for me has always been because of bad CC.  Read this to learn more about this, including what you should do to get rid of it: http://sims3.crinrict.com/en/custom-content-cc/bad-cc

what do you mean by outdated mods?

So even though the game still plays fine with the custom content installed, it is still the reason the new custom content I am trying to install won't work??

I am so confused!!

Mods are stuff people add to their games to change gameplay.  These usually have to be updated for the correct patch version.  You might not have any if you've never downloaded any so don't worry about this if you haven't added any.

My guess as to the bad custom content is it's the new stuff you're trying to download since it happens when you click the "Downloads" button.  Go to Documents>Electronic Arts> The Sims 3> Downloads.   That folder should have anything you're trying to download. You can delete anything that has a sims3pack ending from there (not the .bin files!). 

If you don't want to delete all these new items, make a new folder on your desktop and copy/paste any file that has a sims3pack ending from Downloads into this new folder.  Then add one item from that desktop folder into the Downloads folder.  Start the launcher and try installing that one item.  If it goes through without a problem, then that's good.   Go back to your desktop folder and add another item from there to the Downloads folder (and delete the packs you've already installed from there).  Continue doing this, until the launcher starts the error again.  Once it does, then you'll know which item is bad and is causing the problem.

Does this make sense?

Ok kind of!

Basically it does not happen when I click the download button on the sims 3 launcher. It happens when I click on finder/documents/electronicarts/sims3/downloads and attempt to click on one of the files in there. Normally the file then opens the launcher and downloads and installs straight onto the game but now it opens the launcher but comes up with 'unknown error occurred'

I don't think I am making my problem very clear!

Okay, so the launcher doesn't want to start and install files you're clicking in the Downloads folder?   Does it do that for all the different files or only certain ones. 

the launcher pops up but the separate window that normally opens to install the custom content displays the 'unknown error occurred'. It did not do it for all the custom content i previously downloaded but has just started and I have tried atleast 10 different files to see if that makes any difference and it doesn't!!

Does the launcher and your game work normally if you don't try install any other items?  Does this happen if you try install something from the exchange?

I don't normally download items from the exchange, this is happenning with items downloaded from simsresource. And yes my game plays perfectly fine if I don't try and download these new items! The annoying thing is I want to be able to download new custom content to my game.