backup sql db whit entity framework

hi
i have this sp :

USE [CarsDB]
GO
/****** Object:  StoredProcedure [dbo].[EXEC_BACKUP]    Script Date: 05/05/2015 20:38:47 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

ALTER PROCEDURE [dbo].[EXEC_BACKUP]
      ( @BACKUPPATH VARCHAR(250),
  @BKPDATABASE VARCHAR(100))
AS BEGIN
   DECLARE @@STRQUERY NVARCHAR(500)

   SET @@STRQUERY = 'BACKUP DATABASE ' + @BKPDATABASE + ' TO DISK = '
                    + QUOTENAME(@BACKUPPATH, '''');
   EXECUTE SP_EXECUTESQL @@STRQUERY
 
END;

and from c# form i am running this code to execute the sp :
   public static void DoMakeGib()
        {

            try
            {
                using (EF.CarsDBEntities ef = new EF.CarsDBEntities())
                {
                   
                    string FilePath = "C:\\CarsDB.bak";
                    ef.EXEC_BACKUP(FilePath, "CarsDB");
                   
                   
                }
            }
            catch(Exception ex)
            {
                throw new Exception(ex.InnerException.Message);
            }
}

i am geting this error msg :
{"Cannot perform a backup or restore operation within a transaction.\r\nBACKUP DATABASE is terminating abnormally."}

whats wrong ?