I found a "fix" that works for me every time. Go to Device Manager, look for "Ports (Com & LPT)" and under that find the Arduino 101 Serial Monitor COM port. Right-click and select Disable. Once it is disabled, right-click it again and select Enable. When you get back to the Arduino IDE make sure the Board and Port (Tools menu) are still set for the Arduino 101. They usually are. Then try to Run your program again. Occasionally I also have to stop and restart the IDE after resetting the COM port, but these steps do work well for me when I start getting the messages mentioned.