String as output from SP in C++

I can't seem to properly form a CreateParamter statement for retrieving a
string from a stored procedure. The SP looks a bit like this:
---------------------------------------------
CREATE PROCEDURE dbo.qry_MyQry
@l_spec_cd as int,
@s_addr_list_txt nvarchar(2560) OUTPUT

AS
SET NOCOUNT ON

DECLARE @my_email_txt nvarchar(1280)

SELECT @my_email_txt=EmailAddrTxt
FROM tblPhysician
WHERE PhysicianCd = @l_spec_cd

..
..
..


SET @s_addr_list_txt = @s_addr_list_txt + @my_email_txt

GO
----------------------------------------------

Then in my C++ code I have the following:
----------------------------------------------
_CommandPtr cmd("ADODB.Command");
_ParameterPtr param;

email_addr_list = L"";

cmd->ActiveConnection = _epi_conn;
cmd->CommandText = "qry_MsgEmailPhysEmail";
cmd->CommandType = adCmdStoredProc;

//
// get admitting and/or ordering physician email addrs
//
_variant_t var_phy_email;
CString s_phy_email;

//
// setup stored procedure call
//
param = cmd->CreateParameter (_bstr_t("@l_spec_cd"), adInteger,
adParamInput, 4);
cmd->Parameters->Append(param);
param->Value = spec_cd;

var_phy_email.vt = VT_BSTR;
param = cmd->CreateParameter (_bstr_t("@s_addr_list_txt"), adVarChar,
adParamOutput, 2560, var_phy_email);
cmd->Parameters->Append(param);

cmd->Execute(NULL, NULL, adCmdStoredProc);
---------------------------------------------------------------------

I get an exception while doing the second create parameter for the return
string. Not sure if its a a poorly formatted call to CreateParameter,
illegal variable in that call, or some other violation.

Help?!

.

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