Iframe will not be supported on facebook fan pages tab, the strange thing is, it only happened on first load and the you’ll get this error iframe not supported

I just figured out that apps on Fan Pages Tab need an action from user, so then to get an iframe working on tab,

  1. In your Tab Url file i.e. index.php, create a href tag, that will link to somefile.php 
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    <a href="somefile.php">Click here to begin</a>
  2. Edit your somefile.php and insert <iframe> tag or <fb:iframe/> tag 
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    <fb:iframe src="" width="" height="" />
  3. You might want to make a dummy loading image, just to attract user to click the image, 
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       <img src="url to loading image" />
   <a href="somefile.php">Click here to begin</a>

Alternatively using FBJS as shown in this article, 2 simple hacks to create an iframe on a facebook fan page tab

The script from the article look like this,

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    <a onClick="outside_location.setInnerFBML(location_two);" style="cursor: pointer;">
      Click here to launch game.
      <div id="outside_location">
         <img src='[Enter a url to an image here]' /><br /> <fb:iframe width="760" height="760" frameborder="0" src="http://www.facebook.com/MotherStore" /> 
      </div>
    </a>
   
    <fb:js-string var="location_two">
         <fb:iframe width="[With of iFrame]" height="[Height of iFrame]" style='margin-top: -50px; margin-left: -40px; margin-bottom: -40px; margin-right: -50px;' frameborder='0' src='[Enter the source of the iFrame here]' scrolling='no' />
    </fb:js-string>
   
    <script type="text/javascript" charset="utf-8">
    var outside_location = document.getElementById('outside_location');