Varien_Autoload fails at checkout for Meanbee_Royalmail

I've just installed the Royal Mail module, all appears fine on the admin side of things, but when going through the checkout process, as soon as I get to the Shipping Method step I'm chucked over to an error page that begins:

Warning: Varien_Autoload::include(Meanbee/Royalmail/Model/Shipping/Carrier/Royalmail/.php)

I've reinstalled the module, no change. Running the default Magento theme. Running Magento ver. 1.3.2.3, all extensions are also up to date.