title: Install Xcode 3.2.3 w/ iPhone SDK 4, get "Base SDK missing", can't see other SDKs
body: <p>I created this community wiki to bind together a number of
  other Q/A's I've seen here on SO. If you're here, you've probably
  installed the final version of Xcode 3.2.3 with iPhone SDK 4 (<a href="https://developer.apple.com/iphone/download.action?path=%2Fiphone%2Fiphone_sdk_4__final%2Fxcode_3.2.3_and_iphone_sdk_4__final.dmg" rel="nofollow noreferrer">download
  link</a>, reg reqd), and then encountered one or both of these problems:</p>
  
  <ul>
  <li><p>In your previously working Xcode iPhone project, you get "Base SDK Missing" somewhere. Something like this:</p>
  
  <p><img src="https://i.stack.imgur.com/j9itE.png" alt="Ruh-roh!"></p></li>
  <li><p>In a related but more general observation, none of the previously available panoply of Device or Simulator SDK choices (e.g. 3.0, 3.1, 3.1.3, ...) is available where you used to see them.</p></li>
  </ul>