stored procedure from SQL Server in PHP

I need help running a stored procedure from SQL Server in PHP. PHP is running on a Unix/Linux server. We cannot get OUTPUT variables to return in PHP. The following is the PHP code:

$conn = mssql_connect('server','user','pass');
    mssql_select_db('db', $conn);

    $procedure = mssql_init('usp_StoredProc', $conn);

    $tmpVar1 ='value';
    $tmpVar2 ='value2';

    $outVar1 ='';
    $outVar2 ='';

    mssql_bind($procedure,"@var1", $tmpVar1, SQLVARCHAR,false,false);
    mssql_bind($procedure,"@var2", $tmpVar2, SQLVARCHAR,false,false);

    mssql_bind($procedure,"@outVar1", $outVar1, SQLVARCHAR,true);
    mssql_bind($procedure,"@outVar2", $outVar2, SQLVARCHAR,true);

    mssql_execute($procedure,$conn);print($outVar1);print($outVar2);

The stored procedure looks like so :

    SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

ALTER proc [dbo].[usp_StoredProc](@var1as varchar(36),@var2as varchar(10),@outVar1 varchar(36) OUTPUT,@outVar2 varchar(36) OUTPUT )asselect distinct @outVar1= row1,@outVar2= row2from table1where column1 =@var1and column2 =@var2

Can anyone tell me why $outVar1 and $outVar2 are not being populated? Thanks a lot for any help!