Hi I have the following code:

Transaction manager = new Transaction(System.Data.IsolationLevel.ReadCommitted, "SynchronizeCustomerList");

try
            {
                 foreach (CustomerEntity customer in customerList)
                {
                        customer.ExportedDate = DateTime.Now;
                        manager.Add(customer);
                 }
            manager.Commit();       
            }
           catch
            {
                manager.Rollback();
                throw;
            }
            finally
            {
                manager.Dispose();
            }

How do I save the customers in transaction?

You still need to call the entity's save method after adding it to the transaction. That way the commit will have an action to commit.

Transaction manager = new Transaction(System.Data.IsolationLevel.ReadCommitted, "SynchronizeCustomerList");

try
            {
                 foreach (CustomerEntity customer in customerList)
                {
                        customer.ExportedDate = DateTime.Now;
                        manager.Add(customer);
                        customer.Save();
                 }
            manager.Commit();       
            }
         catch
            {
                manager.Rollback();
                throw;
            }
            finally
            {
                manager.Dispose();
            }

I have tried that, but i doesn't save. If I debud and add a break-point at "manager.Commit(); " it never get that far. I dont get an error, it just stops debugging like everyting is OK.

If I debud and add a break-point at "manager.Commit(); " it never get that far. I dont get an error, it just stops debugging like everyting is OK.

Strange, does it get to the catch block, or the finally block ? Is there anything showing in the output window.

You may try to enable tracing to get to see what's happening in LLBLGen Pro code. Refer to the LLBLGen Pro manual: "Using the generated code -> Troubleshooting and debugging"