I solved the problem. I will trying to explaining the problem. I have a parametric class “based agent”. Inside the class i have methods who can run the monitors and drivers. When the test it’s starts , in the first thing i will run all monitors. Then i will give an initial reset to DUT. In this task i have on the end an "disable fork ". Probably you will not understand verry well, but can give some explications about “disable…fork” in classes instance. I know, “disable label” in class instaces disable all tasks from all instances with that label,but how works " disable fork " ?