des_decrypt and des_encrypt question

[shamsingh]

Whye would the following return NULL:

select des_decrypt(des_encrypt('sample','mykey1'),'mykey1');


Whenever I try just inserting into a BLOB using des_encrypt I also get a NULL when
selecting the column using des_decrypt . Do I need to enable encryption when starting mysql or something?
The examples in the docs seem pretty straight forward and I copied them character for character.

Thanks for you help.