Good Morning funcourt,
The first thing I would suggest for the iTunes error message you are receiving would be to update your OS X to the latest version, which is OS X 10.11.2.
Download OS X El Capitan 10.11.2 Combo Update
Another common troubleshooting step would be to start your computer in Safe Mode
OS X El Capitan: Start up in safe mode
Starting up in safe mode may help you diagnose problems you’re having with your Mac.
Important: To print these instructions, click the Share button 
in the Help window, then choose Print.
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Choose Apple menu > Shut Down.
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After your Mac shuts down, wait 10 seconds, then press the power button.
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Immediately after you hear the startup tone, hold down the Shift key.
You should press the Shift key as soon as possible after you hear the startup tone, but not before.
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Release the Shift key when you see the gray Apple logo and progress indicator.
To leave safe mode, restart your Mac again, but don’t hold down any keys during startup.
Start up in single-user mode
Ways to start up your Mac
Last Modified: Sep 30, 2015
If these two steps don't resolve your issue, try creating a New User account to isolate whether this issue is with your user account or if it is system wide.
How to test an issue in another user account on your Mac
You can figure out if unexpected behavior is related to user file or setting by trying to reproduce the issue from another user account. This process includes creating a new user account, logging in to it, and testing for the issue.
Create a test user account
- From the Apple menu, choose System Preferences.
- Click the Users & Groups icon in the System Preferences window.
- Click the lock icon, then enter an administrator name and password.
- Click the Add button (+) below the list of users.
- Choose a type of user from the New Account pop-up menu.
- Give the user a full name, account name, and password.
- Click OK.
- Close the System Preferences window.
If there are documents from your original user account that you want to test with, place a copy of these items in the Shared folder in the Users folder. Press the Option key while dragging a file to this folder to create a copy.
Log in to the test user account
Log out of your current user account by choosing Log Out from the Apple menu, then log in to the new account you created. If you're prompted to sign in with your iCloud account or Apple ID when you log in, skip this step.
Try reproducing the issue
Try the same steps that caused the unexpected behavior to appear before. For example, if you were unable to print, try printing from this user account. If you were unable to connect to the Internet, try browsing a website from this user account.
If you were using any specific settings that testing depends on (such as using a specific email account or iCloud account) set up the same account in the test user. For email and most other settings you can use the Internet Accounts pane in System Preferences to set up these kinds of accounts. If files from your home folder are needed for testing, copy them to Shared folder in the Users folder (/Users/Shared). After logging in as the test user, copy these items to the same location in the test user's home folder to test with.
If performing the same steps in a test user account doesn't result in the same unexpected behavior, you most likely don't need to reinstall any apps or OS X.
- If an issue only happens in one app, check the app's documentation or support website for instructions on troubleshooting specific preference or setting files.
- If you need help with a specific alert message or issue, search the Apple Support website for the text of the alert message you're seeing.
If the same unexpected behavior happens in more than one user account on your Mac, try checking for software or hardware issues.
After you've finished testing, log out of the test account by choosing Log Out from the Apple menu. Then log in to your original user account.
You can remove the test user account you created when you're done. Make sure you're completely finished testing, and that you don't need any of the files or settings you created or copied there before you remove it.
If you need more help with a software or hardware issue, contact Apple Support. If you work with an Advisor, Genius, or service provider to resolve an issue, be sure to mention any steps you've already tried and the results. Also mention any alert messages you've seen as part of the issue. You can take a screenshot of any messages that appear so you can refer to them later.
Last Modified: Jul 9, 2015
Take care,
