pig script failed to validate: java.lang.RuntimeException: could not instantiate 'org.apache.pig.piggybank.storage.DBStorage'

Question

I'm trying to output a pig script with 3 fields to a PostgreSQL database. When I dump the output, the script works fine. However when I use the DBStorage() method:

register /$directory/postgresql9.4-1201.jdbc41.jar;
register /usr/lib/pig/piggybank.jar;
(removed for privacy purposes)
order_product = order count_product by post_product_list, datew;

store order_product into '$dbschema.$dbtable'
    using org.apache.pig.piggybank.storage.DBStorage('org.postgresql.Driver',
    'jdbc:postgresql://$server:$port/$database',
    '$user',
    '$pass',
    'insert into $dbschema.$dbtable values (?,?,?)');

When I run the above script, I recieve this error:

pig script failed to validate: java.lang.RuntimeException: could not  instantiate 'org.apache.pig.piggybank.storage.DBStorage' with arguments '[org.postgresql.Driver...

I've checked my syntax in DbStorage multiple times and it looks fine. Could anyone offer a word or two?

Thanks!