AWS Redshift does not by default have an aes_encrypt() function. It is possible that in your Aginity environment, a User Defined Function was used to create the aes_encrypt() function that you are referencing. You can confirm if the aes_encrypt() function exists as a UDF in your Redshift instance by querying the pg_proc system catalog table in Redshift. Something like this:
select * from pg_proc where proname ilike '%<name_here>%'
Once confirmed that the aes_encrypt user defined function exists, if you are accessing the same Redshift instance that you are using with Aginity, can you confirm that you are using the same Schema and Database? If you are connecting to a different Schema or Database, then you either need to create the UDF in the same schema that you are using with Matillion ETL or you will need to fully qualify the database and schema of the UDF in the Calculator component.