If you are still having this problem with the site that you have defined in DW you should try defining a new site with new folders. The problem is one with a particular site, defining a new one should relieve the issue.
The error you are getting is a DW one, I don't know of any silver bullet answer for the problem other than deleting the mmServerScripts folder or defining a new DW site. If these do not work for you then you might need to get some assistance from Adobe support.