Some problems occurred when executing the task:
build-propel.xml:479:1: Duplicate table found: propel.
build-propel.xml:465:121: Execution of the target buildfile failed. Aborting.
If the exception message is not clear enough, read the output of the task for more information

So when you’re reverse engineering a database schema, you’ll likely get this error if you have plugins installed and you try to do a propel:build-model. For instance, if you have a an existing database and you’re doing a ./symfony propel:build-schema, it will go in and create a new schema.yml for you.  But, you have tables in there that the plugins will take care of, so there will be a conflict.  To fix this, you should go into the generated schema.yml and clear out the additional tables.  Then run the build-model again.