ums0 diconnections

[Barbara]

Sometimes my mouse seems frozen, then it become responsive again after few 
seconds.
The following lines are added in /var/log/messages:

Jan  4 16:52:59 satanasso kernel: ugen1.2: <Logitech> at usbus1 (disconnected)
Jan  4 16:52:59 satanasso kernel: ums0: at uhub1, port 2, addr 2 
(disconnected)
Jan  4 16:52:59 satanasso hald[1508]: 16:52:59.420 [W] hf-devd.c:379: 
malformed devd event: 
Jan  4 16:52:59 satanasso hald[1508]: 16:52:59.435 [W] hf-devd.c:379: 
malformed devd event: 
Jan  4 16:53:01 satanasso kernel: ugen1.2: <Logitech> at usbus1
Jan  4 16:53:01 satanasso kernel: ums0: <Logitech Optical USB Mouse, class 
0/0, rev 2.00/3.40, addr 2> on usbus1
Jan  4 16:53:01 satanasso kernel: ums0: 3 buttons and [XYZ] coordinates ID=0
Jan  4 16:53:02 satanasso hald[1508]: 16:53:02.439 [W] hf-devd.c:379: 
malformed devd event: 
Jan  4 16:53:02 satanasso hald[1508]: 16:53:02.440 [W] hf-devd.c:379: 
malformed devd event: 

As far as I can remember, this is happening since about a month.
I don't think that it's a hw problem, could it be a sw one?
BTW, I see similar error from hald when, for example, I plug in USB drives.

Thanks
Barbara