It is not problem with updating (thread provided by zerozero) but problem that main window of update manager doesn't show up.
I got same problem, here how it happens:
- i click on icon in tray, or click Update Manager in menu
- give my password
- pops up onlysmall window checking for updates
- that window closes
- all the time doesn't show main window of UM - the one showing list of available updates and its level
I have to try open UM like 3 or 5 times before main window shows up - and it happens whether there are updates or there aren't any.
If i manage to open main window of update manager, then all updates run fine.





