Includes are completely removed now - the issues are within the forum HTML/templates. The validator completely gives up when it gets to the calendar.
It begins with an extra </td> after the top menu links, that closing column could be what starts the cascade of errors.
The includes I use have been used for 10+ years now without change, they have been validated many many times, beginning when I wrote the valid template files way back when.
I could hunt it down for you, but then what would you do?
