Schema not getting installed
I got caught out in Drupal 7 by the fact that you don't need to call drupal_install_schema.  Also, hook_install should now be used to perform actions on your tables, rather than set them up.

Drupal 7 sees your schema and installs it automatically when your module is activated, so because you're calling it manually, it's trying to install the schema twice.

This might help explain it a bit.

Also, try checking in your database to see if the tables already exist.  If it's installed incorrectly, Drupal might be seeing the tables and thinking they're correct when actually they're not.