This type of error usually happens when an already installed extension has updated the menus file for Dreamweaver and the file is no longer updatable. There is likely some change in the file that makes it not recognized as being able to update or something like this.
The only real way to redo this file is to remove all of the extensions you have installed and reinstall them. The error may still occur for you though even after this. The next step up would be to completely remove the configuration folder and have it be recreated, this would also force you to re-install all of your extensions.
It is possible that not even this will resolve the issue though, in which case a re-install of DW may be needed. The problem with this error is that it is usually a sporadic one that cannot be reproduced and therefore does not have a definite method to deal with it.
If you would like to delete your configuration folder to see if that will help eliminate the issue here is a link to a post that gives the exact instructions for this:
showpost.php?p=12293&postcount=2
