You should look for similar keys with a different browser if you don't use Firefox. That .reg script is a standard Firefox fix for that error message. Is there a ddeexec in the registry for Opera? You can always use something like ERUNT to back up your registry before experimenting. In the script the minus sign means to delete the entries.
Whatever you use, do something so you can put the Registry back the way it was, restore point or ERUNT or some other method.
Whenever I do a reinstall of Firefox I get that error(at least that happened on v. 2.x Firefox) and I'd have to run that script again. It shouldn't hurt anything to delete those keys. The backup is just to be backed up.
