VirtualWire or String causes arduino to hang

Using Arduino Programming Questions
8 
char Sensor1CharMsg[4]; 
...

void dataRX()
{
  ...
  uint8_t buflen = VW_MAX_MESSAGE_LEN;

  // Non-blocking
  if (vw_get_message(buf, &buflen)) 
  {
    ...
    // Message with a good checksum received, dump it. 
    for (i = 0; i < buflen; i++)
    {            
      // Fill Sensor1CharMsg Char array with corresponding 
      // chars from buffer.   
      Sensor1CharMsg[i] = char(buf[i]);
    }

Classic buffer overflow bug. Even if you have increased Sensor1CharMsg to 5 elements, the version of VirtualWire.h I just looked at (1.9) defines VW_MAX_MESSAGE_LEN as 30. So the above code will write beyond the end of the buffer, if you receive a message more than 4 or 5 bytes long. Never trust input to be in the expected form, even if it is (in theory) under your control.