Grant permissions to execute Stored Procedure

I have a stored procedure that looks somewhat like this:

CREATE PROCEDURE Build_Test (@Client varchar(30) = " ")
AS
begin

 set nocount on
 
 declare @sql varchar(8000)

 set @sql = 'CREATE TABLE dbo.[' + @Client + '_Test] (' +
     '[Column1] [char] (8) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL ,
      [Column2] [char] (3) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL
) ON [PRIMARY] '
 
 execute (@sql)
 set nocount off
end

Set @sql='GRANT  REFERENCES ,  SELECT ,  UPDATE ,  INSERT ,  DELETE  ON [' + @Client + '_Test] TO [nsmith]'  
Exec(@sql)

Set @sql='GRANT  REFERENCES ,  SELECT ,  UPDATE ,  INSERT ,  DELETE  ON [' + @Client + '_Test] TO [public]'
Exec(@sql)

Set @sql='GRANT  REFERENCES ,  SELECT ,  UPDATE ,  INSERT ,  DELETE  ON [' + @Client + '_Test] TO [ttoms]'
Exec(@sql)

Set @sql='GRANT  REFERENCES ,  SELECT ,  UPDATE ,  INSERT ,  DELETE  ON [' + @Client + '_Test] TO [ISTService]'
Exec(@sql)
GO



I also need to grant execute privileges to run the sp, since I will be calling it from an ASP page:

GRANT  EXECUTE  ON Build_Car TO [nsmith]

GRANT  EXECUTE  ON Build_Car TO [public]

GRANT  EXECUTE  ON Build_Car TO [ttoms]

GRANT  EXECUTE  ON Build_Car TO [ISTService]

I need to run the GRANT statements inside the procedure.  However, they are not triggering when I run the sp.  I had them placed right after this:

CREATE PROCEDURE Build_Car (@Client varchar(30) = " ")
AS
begin

Not working :).  What to do?

Thanks,

IPT