HELP .. I am having a similar problem .. I am using Dreamweaver 8 (i know but i am in love with the layout view and don't touch cs5 yet) save the criticism .lol
Well anyways i just got a new cpu and when I open certain sites up on my new cpu WIN 7 64bit I get the Markup Invalid because its overlapping or unclosed tag . error .. and my display mode is all messed up .. These sites are online and view fine in the browser .. but i wont be able to update them ..
I have added screen shots of the error .. I have only added a few of my sites to the new Dreamweaver so far .. and am afraid to add more until i figure this out .. But anyways some work fine .. and even as you will see in my screen shots .. one that views fine has the same exact code as one that has the error .. .. I will also provide URL's to the sites online in case you need to look at the code closer .. the one that is a example of viewing fine is a site in progress so will only be the home page ..
Thanks in advance for any help ..
Sites from screen shots 1 http://www.granitepeakdev.com/
2-3 - http://www.caplures.com/
and the one with same code but views great .. http://www.waveswebdesign.com/gedc/