SQL Server Admin 2014 :: Using Column Encryption With Symmetric Keys

I am trying to implement the column encryption on one of the tables, have used the below link as the reference and got stuck at the last step.

[URL] ....

I have completed the following steps so far.

- CREATE MASTER KEY ENCRYPTION BY PASSWORD = ‘myStrongPassword’

- CREATE CERTIFICATE MyCertificateName
WITH SUBJECT = 'A label for this certificate'

- CREATE SYMMETRIC KEY MySymmetricKeyName WITH
IDENTITY_VALUE = 'a fairly secure name',
ALGORITHM = AES_256,

[Code] .....

Example by using the function

EXEC OpenKeys

-- Encrypting
SELECT Encrypt(myColumn) FROM myTable

-- Decrypting
SELECT Decrypt(myColumn) FROM myTable

When I ran the last command :

-- Decrypting
SELECT Decrypt(myColumn) FROM myTable

I get the following error :

Msg 257, Level 16, State 3, Line 2
Implicit conversion from data type nvarchar to varbinary is not allowed. Use the CONVERT function to run this query.

Where will I use the convert function, in decrypt function or in select statement?