Can not correctly call mysql stored procedure via .net C#

Hi.

I'm use to writing stored procedures in sql server and not venturing into mysql.  But i'm getting this error when I call the sproc from my .net code:
"You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use"
BUT if I call my sproc from mysql browser it works fine.   Here's my create script for the sproc:
**********
DELIMITER $$

DROP PROCEDURE IF EXISTS `uspValidateUser`$$

CREATE   PROCEDURE `uspValidateUser`
(
    `@UserName` VARCHAR(50)
)
BEGIN

IF Not Exists (SELECT `UserId`
             FROM   `Users`
             WHERE  `UserName` = `@UserName`) THEN
        SELECT 0 As `Error`;
    ELSE

        /********************************************
        * UPDATE LastLoginDate FIELD
        ********************************************/

        UPDATE  `Users`
           SET  `LastLoginDate` = NOW()
         WHERE  `UserName` = `@UserName`;

        /********************************************
        * GET return
        ********************************************/

        SELECT
                U.`UserId`,
                U.`UserName`,
                U.`Password`,
                U.`Salt`,
                U.`UserDemographicsId`,
                R.`Role`,
                U.`LastLoginDate`,
                U.`LastUpdatedDate`,
                U.`LastUpdatedBy`,
                U.`CreatedDate`,
                U.`CreatedBy`
        FROM    `Users` U
        JOIN    `Roles` R
          ON    U.`RoleId` = R.`RoleId`
        WHERE   U.`UserName` = `@UserName`;

    END IF;

END$$
**********

Now here is my C# code (using the .net connector supplied by Mysql):
**********
        public User ValidateUserCredentials(string username)
        {
            User user = null;
            const string PROC_NAME = "uspValidateUser";

            MySqlParameter[] sqlParams = new MySqlParameter[1];
            sqlParams[0] = new MySqlParameter("?UserName", MySqlDbType.VarChar);
            sqlParams[0].Direction = ParameterDirection.Input;
            sqlParams[0].Value = username;

            using(MySqlDataReader sqlReader = MySqlHelper.ExecuteReader(_ConnectionString, PROC_NAME, sqlParams))
            {
                if (sqlReader.Read())
                {
                    user = new User(sqlReader.GetInt32(sqlReader.GetOrdinal("UserId")),
                                        sqlReader.GetString(sqlReader.GetOrdinal("UserName")),
                                        sqlReader.GetString(sqlReader.GetOrdinal("Password")),
                                        sqlReader.GetString(sqlReader.GetOrdinal("Salt")),
                                        sqlReader.GetString(sqlReader.GetOrdinal("Role")),
                                        sqlReader.GetInt32(sqlReader.GetOrdinal("UserDemographicsId")),
                                        sqlReader.GetDateTime(sqlReader.GetOrdinal("LastLoginDate")),
                                        sqlReader.GetString(sqlReader.GetOrdinal("CreatedBy")),
                                        sqlReader.GetDateTime(sqlReader.GetOrdinal("CreatedDate")),
                                        sqlReader.GetString(sqlReader.GetOrdinal("LastUpdatedBy")),
                                        sqlReader.GetDateTime(sqlReader.GetOrdinal("LastUpdatedDate")));
                    return user;
                }
            }

            return null;
        }
**********

I have tried different alterations of the param syntax within the c# code but yet nothing is producing results.    I don't think my sproc code is wrong because I'm able to successfully run it in the mysql browser but maybe someone knows something I don't.  thanks for your help!