Hi. Thanks for reply. I appreciate your opinion on the title. Maybe it is a misunderstanding. I was meaning that such behaviour, rather weird, related to an apparently innocent instruction, was out of the concern of a "user" of B4A, like I and all people here are. We develop products using B4A. We use B4A. We didn't develop B4A. This was what I was meaning. The question was devoted to people (from Klaus answer probably only Erel), that can understand what's happening. You didn't understand the problem, sorry. You just found an empirical remedy. Why putting a Sleep(0) ? If you look to another recent post of mine, you will see that I met a problem just naming a service "s1". Has this a sense? Of course I changed the name and things worked, but I don't say that I have understood why or that I solved the issue In the present case, shall we put a Sleep inside calculations (not so heavy, anyway). By the way it crashes at the beginning, not when such calculation is done ... Or, as usual, I didn't understand what I was doing.. as usual ..Anyway thanks again.