it's because your on 0.6.5 and the package hasn't been updated yet to work with that, there was a lot of api changes in the way you format your package.js file and most packages on meteorite haven't been updated to adhere to the new style yet so they all break.
Recommendation:
1 Use this command to downgrade and wait a few weeks until atmosphere packages get corrected
"The way to downgrade is:
$ meteor update --release 0.6.4.1
... but that won't actually undo the other change that updating your
app to 0.6.5 did. So you'll also want to edit your ".meteor/packages"
file and remove the line "standard-app-packages". "
2 Send a PR to the package creator with an updated package.js file adhering to the api rules listed here
https://github.com/meteor/meteor/blob/devel/History.md
File that needs to be updated:
https://github.com/erobit/meteor-accounts-ui-bootstrap-dropdown/blob/master/package.js