vjandrea:
I mean the serial interface. I tried both the Uno and the Mega 2560 with a Win7 PC and the problem persists.
When i set the COM port baud rate to 115200 in the hardware preferences, and i broadcast from Arduino at 9600, everything works fine.
As soon as i move from that value in Serial.begin(), i.e. 14400 or 11520, i receive garbled text.
I've tested quite a few Arduino and clones (including homemade ones) with 115200 and they all work in Win7 64-bit.
Are you by chance trying to use the serial port of the Arduino UNO in 2 simultaneous connections (1 to the computer and another to the external device) ? If you are, that is not gonna work.
The best for debugging serial devices is the Arduino Mega, because it has 3 serial ports. Use Serial0 for the USB connection and Serial1 or Serial2 to the other device.