I am trying to download Yosemite. Repeatedly getting message:There was an error in the App Store. Please try again later."

Question

I am trying to download Yosemite. Repeatedly getting message:There was an error in the App Store. Please try again later."

Answer 1

That cryptic error message might mean that the payment information in your account is invalid. Check with your credit-card issuer to see whether a charge was denied. If not, see below.
Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
The purpose of this test is to determine whether the problem is localized to your user account. Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”
While logged in as Guest, you won’t have access to any of your documents or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this behavior; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
Test while logged in as Guest. Same problem?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.
*Note: If you’ve activated “Find My Mac” or FileVault in OS X 10.7 or later, then you can’t enable the Guest account. The "Guest User" login created by "Find My Mac" is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.