My New Function Not Found

I issue this command in QA:
CREATE FUNCTION encrypt_pair (@data VARCHAR(14) , @key char(30) )
RETURNS VARCHAR (60) AS
BEGIN
DECLARE @encryptedvars VARCHAR(60)
EXEC master..xp_aes_encrypt @data,@key,@encryptedvars OUTPUT
RETURN @encryptedvars
END

If I run it again, I get an error that it already exists (duh).
Next I run:

select student_id, student_ssn,
encrypt_pair(student_ssn,'000000000000000000000000 00000000') from
student_ssn

and I get the error:
Server: Msg 195, Level 15, State 10, Line 1
'encrypt_pair' is not a recognized function name.
I don't get whats wrong!
Thanks
Rob