lorax - 2:43 pm on Jan 14, 2013 (gmt 0)
I'd do some digging to eliminate any possibility that another program or user error have created the errors. So if they're in GWT then either Google found links to them on your site or you told Google they exist. Have you used a link sniffer to find out what/if pages link to these URLs? Are you using any automated tools to generate an XML file for Google to read and if so have you looked at the XML file?