I had this three times now, but I haven’'t figured out, how exactly it happens.
Spark is still running (says Taskmanager), but it’'s not showing up in the system tray.
Unfortunately, Spark doesn’‘t show it’'s Window, when you launch it again (like some other programs do), so my only choice of action is killing it from Taskman and starting it again.
it may be really hard to get more details about the problem as the TNA stuff uses JNI, so it’'s native c code which seems to have a problem with the TNA.