It looks like it is having a hard time accessing the folder and file specified. If this is the only folder and file that is producing this error you may need to reset your site cache in DW. To do this go to Site > Advanced > Recreate Site Cache. Give this a try to see if it get's you past this error.
Another thing you may want to look at is the local info for your site. If you are testing locally and have local files specified in the testing server portion then you should have this same information specified in the local settings. This way DW will not need to sync to the testing server since it is the same location as your local files.