pgp_sym_decrypt() - error 39000: wrong key or corrupt data

Hi,
    while playing with pgcrypto I ran into a strange issue (postgresql
9.5.3 x86 on Windows 7)

Having a table with a field
dateofbirth text

I made the following sequence of SQL commands
update tbl_p set dateofbirth = pgp_sym_encrypt('2018-06-21', 'AES_KEY')
where codguid = '00000001-0001-0001-0001-000000000001';
OK

select pgp_sym_decrypt(dateofbirth::bytea, 'AES_KEY') as datanasc from
tbl_p where codguid = '00000001-0001-0001-0001-000000000001'
'2018-06-21'

select * from tab_paz where pgp_sym_decrypt(natoil::bytea, 'AES_KEY') =
'2018-06-21'
ERROR:  Wrong key or corrupt data
********** Error **********

ERROR: Wrong key or corrupt data
SQL state: 39000

Can't find reference anywhere...
Any help would be appreciated.
Thanks,
Moreno.-