Helper data not found in custom module

Question

I am getting error: Fatal error: Class 'Mage_Assel_Holidays_Helper_Data' not found

Here is config.xml--

<?xml version="1.0" encoding="UTF-8"?>
<config>
  <modules>
        <Assel_Holidays>
            <version>1.0.0</version>
        </Assel_Holidays>
   </modules>
   <admin>
        <routers>
            <holidays>
                <use>admin</use>
                <args>
                    <module>Assel_Holidays</module>
                    <frontName>holi</frontName>
                </args>
            </holidays>
        </routers>
   </admin>
   <frontend>
        <routers>
            <holidays>
                <use>standard</use>
                <args>
                    <module>Assel_Holidays</module>
                    <frontName>holidays</frontName>
                </args>
            </holidays>
        </routers>
    </frontend>
   <global>
      <helpers>
            <holidays>
                <class>Assel_Holidays_Helper</class>
            </holidays>
      </helpers>
      <blocks>
            <holidays>
                <class>Assel_Holidays_Block</class>
            </holidays> 
      </blocks>
   </global>
</config> 

I have helper class in Data.php in Assel/Holidays/Helper/ folder.

Here is the Data.php

<?php
class Assel_Holidays_Helper_Data extends Mage_Core_Helper_Abstract
{

}

Here is the app/etc/modules/Assel_Holidays.xml--

<?xml version="1.0" encoding="utf-8"?>
<config>
    <modules>
        <Assel_Holidays>
          <active>true</active>
          <codePool>local</codePool>
        </Assel_Holidays>
    </modules>
</config>

I couldn't found out what is the reason behind it.

Answer 1

I am not calling like this Mage::helper('holidays') anywhere

Then you use it indirectly with translation of XML nodes. Please check your system.xml and/or adminhtml.xml files and replace module="Assel_Holidays" with module="holidays"

In XML files (config.xml, system.xml, layout) you can specify if nodes should be translated with the translate attribute. You should also add the module attribute to specify the scope, but here the value has to be the helper alias, not the module name as above.

<one_column module="page" translate="label">
    <label>1 column</label>
    <template>page/1column.phtml</template>
    <layout_handle>page_one_column</layout_handle>
    <is_default>1</is_default>
</one_column>

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