The problem is that the program creates so much RAM usage that after several hours of downloading blocks, it will get a ram access error (forgot the english term). I have 2 GB now. Of course I always use "Quit".
Edit: Now it shows 1,3 GB ram usage in the taskmanager. In a while it will show 1,6666666 TB!
E2: This problem has been there since such a long time, I cannot check my balance since months!