I am using Arduino Duemilanove on Ubuntu 9.10 with IDE version 0017. All was well until three days ago. Since then if I change the serial debug baud rate in the serial debug window to anything higher than 9600 I lose communications with the comm port (error opening serial port 'dev/ttyUSB0'). Once that occurs the comm port is unavailable, Serial Port is grayed out under Tools, and I can no longer upload any sketch or monitor serial output. I can put any serial rate I want in the sketch but if it is not 9600 or lower I have no debug capability.
Once this occurs to get back to being able to upload a sketch I must do this: close the IDE and either delete the ~/.arduino/preferences.txt file in its entirety or delete the line in that file that sets the serial debug rate (serial.debug_rate=xxxxx) Simply closing the IDE does not help and plugging/unplugging the device does not help. When I reopen the IDE I can upload sketches fine. I can also monitor serial debug output as long as the rate set in the sketch is 9600 or less. If I use the IDE but do not try to change the serial debug rate then all is well and on subsequent restarts of the IDE I do not have to delete anything in the preferences.txt file.
I can't point to any major system changes that could account for this. It was working fine then seems to have just happened. I reinstalled java and the ide but to no avail. Dmesg looks good for the ftdi and it does work unless I use the serial debug at more than 9600.