FlexJS

Not sure if I can ask this question here but here it goes.
I am trying to follow instructions described here:
https://cwiki.apache.org/confluence/display/FLEX/Using+FlexJS+with+Adobe+Flash+Builder
and I am having a problem with #8:
In the Flash Builder Preferences menu add this new folder as a Flex SDK.

But FB is not taking this new folder saying it does not contain a Flex SDK.

Any idea?

Thanks