I am trying to login from the admin side of my site. But it is not logging me in with the correct user-name and password provided.

I cleared browser history and tried in other browsers also.

It gives me an error :

Fatal error: Access to undeclared static property: Mage::$_isDeveloperMode in /home//public_html/one/em0113-full-package /app/Mage.php on line 881

Help me to resolve this issue.

  • its really the greatest co incidence that, after posting 1st answer in Aug 24 '15 exactly after 1 year, 2nd answer is posted on Aug 24 '16 ..... Commented Feb 17, 2017 at 9:12

2 Answers 2


I suspect a core hack here. The error is pointing to this lines of code :

public static function getIsDeveloperMode()
    return self::$_isDeveloperMode;

The method simply returns a static property $_isDeveloperMode of the class app\Mage.php. You can find that the definition of that static property in that file itself in line 117 (magento 1.9.1) like this.

static private $_isDeveloperMode = false;

So what you need to do here is, either add this single line inside app\Mage.php or

the best option is replace your BADLY HACKED Mage.php file with the default Mage.php file. You didn't specify the version of Magento used. So use Mage.php file from same version.

  • i replaced the Mage.php its worked.... Commented Aug 24, 2015 at 5:15
  • 1
    @BabyinMagento2 that's it. Happy to hear that it helped Commented Aug 24, 2015 at 5:29

Shouldn't update Mage.php file.

This issue can be easily resolved by either of the following methods:

  1. In index.php look for the following code: if (isset($_SERVER['MAGE_IS_DEVELOPER_MODE'])) { Mage::setIsDeveloperMode(true); }

Change "true" to "false"

2.In .htaccess you should see something like : SetEnv MAGE_IS_DEVELOPER_MODE "true

Comment this code out so it will be #SetEnv MAGE_IS_DEVELOPER_MODE "true

  • Welcome to community , you are absolutely right, Thanks a lot for your guidance, i remember i replaced original Mage.php file , cheers :-) Commented Aug 24, 2016 at 10:21

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