Hard crash when accessing certain members of SerialPort

Hi! I am creating a SerialPort object and opening it. Then I'm accessing the BytesToRead property, at which point Unity implodes and I arrive at the Crash Report dialog. I'd like to avoid that.

Many other properties such as IsOpen seem to work fine. Is there something I'm not catching, or certain things I can't use from .NET or from System.IO.Ports?

More information about my situation:

I'm trying to use a Zephyr HxM heart monitor as an input device in my game. The HxM is a bluetooth device. I have it paired with a Rocketfish bluetooth USB stick. The stick opens three COM ports and the input from the HxM is constantly streaming in through one of them.

My project is configured as .NET 2.0. I'm on Unity Pro 4 on Windows 7.

My script:

 using UnityEngine;
 using System;
 using System.Text;
 using System.Collections;
 using System.Collections.Generic;
 using System.IO.Ports;
  
 public class PortReader: MonoBehaviour 
 {
     List<string> portNames = new List<string>();
     string portName = "COM8"; // THE HEART MONITOR IS CONSTANTLY INPUTTING THROUGH THIS PORT
     SerialPort serialPort;
     
     void Start () 
     {
         serialPort = new SerialPort();
     }
     void FixedUpdate() 
     {
         // OPEN THE PORT (IF NOT ALREADY OPEN)
         try
         {
             OpenConnection();
             print("Port open!");
         }
         catch(Exception e)
         {
             print("Problem opening port! -- " + e.ToString());
         }
         // GET DATA
         try
         {
             int bytes = serialPort.BytesToRead; // THIS LINE CRASHES UNITY
             // int bytes = 133; // THIS LINE DOES NOT
             byte[] comBuffer = new byte[bytes];
             serialPort.Read(comBuffer, 0, bytes);
             print(ByteToHex(comBuffer));
         }
         catch(Exception e)
         {
             print("Problem reading! -- " + e.ToString());
         }
     }
     private void OpenConnection()
     {
         if( serialPort != null && !serialPort.IsOpen )
         {
             serialPort.PortName = portName;
             // THESE SETTINGS ARE ACCORDING TO THE HXM MANUAL
             serialPort.BaudRate = 115200;
             serialPort.DataBits = 8;
             serialPort.StopBits = StopBits.One;
             serialPort.Parity = Parity.None;
             serialPort.Handshake = Handshake.None;
             // THE MANUAL SAYS THE HXM TRANSMITS ABOUT ONCE PER SECOND, SO I GIVE IT A LITTLE MORE THAN THAT BEFORE TIMEOUT.
             serialPort.ReadTimeout = 1200;
             print("Opening port " + portName + "! Time: " + DateTime.Now.ToLongTimeString());
             serialPort.Open();
         }
     }
     private string ByteToHex(byte[] comByte)
     {
         //create a new StringBuilder object
         StringBuilder builder = new StringBuilder(comByte.Length * 3);
         //loop through each byte in the array
         foreach (byte data in comByte)
             //convert the byte to a string and add to the stringbuilder
             builder.Append(Convert.ToString(data, 16).PadLeft(2, '0').PadRight(3, ' '));
         //return the converted value
         return builder.ToString().ToUpper();
     }
     void OnApplicationQuit()
     {
         if(serialPort != null)
         {
             print("Closing port!");
             serialPort.Close();
         }
     }
 }
 

PS This is my first question so let me know if it needs improvement!