Sqlhelper Class Failed To Convert Sql Parameter To A String Error

I'm getting this error and I'm not really sure what is wrong.  I'm using the sqlhelper class which was writen by microsoft, so I figure the code is right.

 Here is code of me passing in the strings.  Yes I tried puttinga .ToString() on the end of the sqlparameters.

public class LoginSelectData : DataAccessBase
{
private EndUser _enduser;
public LoginSelectData()
{
    StoredProcedureName = StoredProcedure.Name.VERIFYUSER.ToString();
}public DataSet Get()
{
DataSet ds;LoginSelectDataParameters _loginselectedataParameters = new LoginSelectDataParameters(this.Enduser);
DataBaseHelper dbhelper = new DataBaseHelper(StoredProcedureName);
ds = dbhelper.Run(base.ConnectionString, _loginselectedataParameters.Parameters);
return ds;

}public EndUser Enduser
{
get { return _enduser; }
set { _enduser = value; }
}

}

public class LoginSelectDataParameters
{
private EndUser _enduser;
private SqlParameter[] _parameters;public LoginSelectDataParameters(EndUser userinfo)
{
this.Enduser = userinfo;

Build();

}

 private void Build()
{

SqlParameter[] parameters =
{new SqlParameter("@username",this.Enduser.Username),
new SqlParameter("@password",this.Enduser.Password)

};

Parameters = parameters;
}public SqlParameter[] Parameters
{
get { return _parameters;
set { _parameters = value; }

}
public EndUser Enduser
{
get { return _enduser; }
set { _enduser = value; }
}

}