Subscription - by: I-Tecnology

Hi,
I have a problem with Subscription.
Here my code:

With this code I make a subscription to an item (a bit value).
It seems all is ok, as I start my programm it works fine. But if there are no changes for about 1minute, next changes are lost. No more changes are detected
Do you have any ideas of the problem?

I'm using latest version of OpcLabs library (today I download it to upgrade).
Framework is 4.5.2
OPC server is Topserver 5.16.728

I have also used this ( but nothing has changed):
Whitch is the difference beetween SubscribeDataChange and SubscribeMonitoredItem?

best regards