Did you ever solve this (since posting back in 2012)? Either way, I'll offer some thoughts in case others may find the question and still seek an answer.
Thanks for the link to my blog post, btw. Sorry it didn't help then.
You refer to other comments reflecting the problem with no solution. Did you happen to revisit the comments since then? You may find new info.
In addition, did you happen to have more than one browser open looking at the Admin? That could cause the problem (as each browser creates different cookies to track the "user" who is logged in).
Or did you happen to have more than once instance of CF against which you were logging in, but using perhaps the same IP address (but different ports) for their CF Admin? That would cause even one browser to send the same cookies to the different instances, which may cause the instance to reject/rotate them to protect against session fixation.
Indeed, to that point, did you ever try using the coldfusion.session.protectfixation jvm flag to see if that helped (https://www.petefreitag.com/item/815.cfm), though it may be overkill to solve this one problem.
FInally, did you happen to see the later post I did, which showed how some problems are due to duplicate cookies? (http://www.carehart.org/blog/client/index.cfm/2014/4/10/CF_Admin_error_about_error_accessing_this_page)