From the error, it is obvious that, you are using some custom extension in the footer and there is a helper call like this somewhere inside the footer section.
Mage::helper('icategory');
Since that extension is wrongly confgiured the helper section, Magento couldn't find the relevant helper corresponding to this call. So you should find the extension and add this inside it.
<config>
<global>
<helpers>
<icategory>[Namepspace]_[Module]_Helper</icategory>
</help
</config>
This is all we can say about this error right now. To get more info, you should put more details to the question
[Namespace]_[Module] should replace with the correct extension name