The error is telling you that you are missing a column in the orders table called is_guest_order. Again, I don't know why upgrading OPC versions hasn't updated the orders table to add this column, I haven't looked at the code. But, to get you rolling on your merry way, you can easily add this column.
Code:
ALTER TABLE `orders` ADD COLUMN `is_guest_order` tinyint(1) NOT NULL DEFAULT '0';
You can paste this into tools>install sql patches.