Thank you for your effort i will try to answer your questions the best i can.

1.the main program only creates the main form from which 3 other forms are opened.
Each of the background workers create one instance of Form2.

all 3 background workers are started even before the main application starts(main form).after the background worker does instance of Form2 and some other variables it goes in the loop where he collects some informations and after that i call an event which updates the instance of form.The background worker is all the time collecting data and updating the instance so he never shuts down or stops.He is in infinite loop.

The identification of problem.

When i open one of those 3 windows from main window and when i close it.If i open the same window(same instance) again everything is OK but when i open a window and close it and try to open an ANOTHER window(another instance of Form2) everything stops.

Each of 3 windows are opened with button click events from main form,and the background workers are started immideatly and are running all the time collecting data from 3 instances. when the user decides to show them they should be shown with the latest data from background worker.That is the main idea.

Thanks for your help and i hope this will give you a clue of my problem