There is a version in info file '7.x-2.0-alpha2+2-dev' in last dev version.
Which is incompatible with dependency format - http://drupal.org/node/542202 (see for example http://drupal.org/project/twitter_bootstrap_ui).
I assume it should be named like '7.x-2.x'.

Comments

Status:Active» Closed (works as designed)

The drupal.org packaging script injects this version string. As you can see, it is not contained in the source code:
http://drupalcode.org/project/libraries.git/blob/HEAD:/libraries.info

In any case, the claim that this version string would be incompatible with dependency versions is not true. Drupal core (actually PHP) handles the versions correctly.

You likely want:

dependencies[] = libraries (>=2, <3)

The documentation page http://drupal.org/node/542202 might be outdated.