I don't have DW8, but this is what I do when I get strange problems:
1. Exit DW
2. Delete cache
3. See if that clears errors
If not:
1. Exit DW
2. Start Extension Manager
3. Make sure I have the latest version
4. Uninstall extension (even if it's the same version)
5. Install latest version of extension (answer yes to overwrite all)
6. Delete cache
Sometimes extension manager screws something up the first time.
If the errors get worse or random, it's time to move to step two - delete configuration folder and reinstall extensions. If you have a large number of extensions you might want to wait to see if someone else has solved this error before.