There is an upgrade error from v4.5.8 to v4.6.11. Even i tried to upgrade to v4.6.0, it fails. Please suggest an solution how to fix it. I upgrade the existing database from v4.5.5 to 4.5.8 which is running without errors.
Jitendra's comment is correct - it should be posted as an answer!
As for your second error, that's caused by skipping the first error. The SQL for 4.6.alpha1 includes the command to create the "civicrm_recurring_entity" table. When you skip the rest of the 4.6.alpha1 SQL, you're creating the circumstance that leads to the second error.