I connect to my Samsung Galaxy S2 by USB from my Ubuntu 11.10 computer. It was working fine up until a few days ago.
Now, for reasons I can't determine, whenever I try to copy any files using the file manager (Nautilus), the transfer always stops at around 10 to 15% done, and then it hangs. The only way to kill the process is to disconnect the USB physically.
I thought maybe this was a problem with the SD card having an error, so I reformatted it, but that hasn't helped. Also, the same thing happens with the Galaxy's internal USB storage as well.
This seems to be an Ubuntu problem, as I tested transferring files on a Windows computer and it went through without any issues.