Error generated when clicking on insert image in a CMS page

Question

While in a CMS page, when I click on "Insert image", it creates the following error. This error is repeated for the number of images displayed in the popup window! If the pop up displays 6 images, the error is repeated 6 times in the system.log.

But clicking on the "Insert image", pointing to the same folder, the second or third time the error is not generated.

What is causing this? How can I prevent this error from being generated? Is this some how being cached?

Note: I have tried turning off all my third party extensions, but it produces the same errors.

2016-08-20T22:26:59+00:00 DEBUG (7): HEADERS ALREADY SENT: <pre>[0] /home/magento/app/code/core/Mage/Core/Controller/Response/Http.php:52
[1] /home/magento/lib/Zend/Controller/Response/Abstract.php:768
[2] /home/magento/app/code/core/Mage/Core/Controller/Response/Http.php:84
[3] /home/magento/app/code/core/Mage/Core/Controller/Varien/Front.php:184
[4] /home/magento/app/code/core/Mage/Core/Model/App.php:354
[5] /home/magento/app/Mage.php:684
[6] /home/magento/index.php:91
</pre>

Answer 1

The problem is caused by the fact that headers are sent twice when your code is called. You probably have a module doing this as its not the default Magento behavior.

I suggest you have a look at the two answers from Alan Storm here to debug the issue: https://stackoverflow.com/questions/4670031/magento-debug-headers-already-sent-error