This is the winfilecache.dat issue or macfilecache.dat issue if you are on a mac. Search the forums for more details, but essentially you need to close dreamweaver and delete a cache file.
Then when you restart Dreamweaver the problem will be gone. It isn't actually a problem with the code or an an extension. It is a problem with Dreamweaver thinking there is a problem when there isn't. We have reported this to the adobe team and they have assured us it will be fixed in their next update.
The file should exist in your user configuration folder. On PC type "%appdata%" into explorer to find the correct application directory, then browse down to the Dreamweaver version and find the Configuration folder. That is where you will find the offending cache file.