OnePica AvaTax - fix for hash key serialization error in app/code/community/OnePica/AvaTax/Model/Avatax/Estimate.php

Estimate.php

    /**
     * Generates a hash key for the exact request
     *
     * @return string
     */
    protected function _genRequestKey() {
        $request = @(string)(array)$this->_request;
        $hash = sprintf("%u", crc32(serialize($request)));
        Mage::getSingleton('avatax/session')->setLastRequestKey($hash);
        return $hash;
    }