Ahh, make sense! Just saw the note at the top of the GitHub site.
[ATTACH=CONFIG]25677[/ATTACH]
After that, I downloaded my 3.3 Flex Viewer from here, now it's working perfectly!
[ATTACH=CONFIG]25678[/ATTACH]
Have also tried Arcgis viewer 3.4 on my Flash Builder, no more errors.. 🙂
Thanks!