I'm also seeing the RSSUpdate.js error (image attached).
I'm running Dreamweaver CS6, and the extensions I have are:
Design Extender 1.1.1
WebAssist Free Tools 1.0.1
Jeffrey Zeldman's Web Standards Advisor 1.0.2
Data Bridge 1.0.8
I should also mention that I've deleted the cache file, reset my workspace, set Memento to Never show on startup AND Disabled all RSS Feeds! The error message persists.