Every time I install a new extension from Magento commerce and I return to admin from Magento connect it shows Fetal error class not found in mage.php

please help me with this.

Fatal error: Class 'Qualityunit_Liveagent_Helper_Data' not found in C:\wamp\www\magento\app\Mage.php on line 548

  • 1
    Qualityunit_Liveagent In this extension either helper class is not declared. or in XML file helper is not declared properly so it is showing such error. Commented Mar 22, 2017 at 5:49

2 Answers 2


This issue arise only in two cases.

1) You are creating any custom module in magento.
2) Your compiler having same issue.

In your case you are facing issue with default magento extension installation. So it should be second option. Here is solution for second case.

From System, Tools disable or re-compile Compilation. If you can't access to admin interface you can disable it by SSH:

php -f shell/compiler.php -- disable
php -f shell/compiler.php -- clear
php -f shell/compiler.php -- state

The final output should appear like:

Compiler Status:          Disabled
Compilation State:        Not Compiled
Collected Files Count:    0
Compiled Scopes Count:    0

For First case, you will surely get help from here.



there are 2 other possibility for this error except compiler issue discuss by @Pankaj.

this class does not exist.

for 1st case check file should be at there.


this Data.php file should be this location

2Nd possibility

May be your module is disable from System->Configuration->Advanced->Advanced

check if this module is disable

OR check


In this file check if <active>false</active> is there or not if this node is false then set true and check once again

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