you should you use following code
$configValue = Mage::getStoreConfig(
'sectionName/groupName/fieldName',
Mage::app()->getStore()
);
Mage::app()->getStore()
this will add store code in fetch values so that you can get correct configuration values for current store this will avoid incorrect store's values because magento is also use for multiple store/views so must add store code to fetch anything in magento.
if we have more then one store or multiple views configured then this will insure that we are getting values for current store