PL/SQL doesnt recognize privileges granted to roles

My procedure has a create database link in it:

v_exe := 'create database link temp_security_monitor '               ||
         'connect to '  p_username  ' identified by '  p_password    ||
         ' using '  ''''  p_tns_string  '''';          

if v_debug = TRUE
    then  dbms_output.put_line (v_exe);
end if;

execute immediate v_exe;

This was failing:

Unexpected error-1031 ORA-01031: insufficient privileges

SQL> conn <a href="mailto:sys@db">sys@db</a> as sysdba
Connected.
SQL> grant create database link to system;
Grant succeeded.

Then all was hunky-dory