EV3 won't connect through bluetooth anymore
You should always be using the latest firmware. If you have an EV3 brick that was produced in mid 2015 or later, it may have a newer Bluetooth chip that requires firmware v1.07 or higher. See https://bricks.stackexchange.com/a/7237/3498 for an unofficial firmware changelog.

If updating the firmware does not fix the problem then the name of the comm port probably changed. This is something like "COM1" or "COM5". Look in the Device Manager to see what comm port is assigned to your EV3 and make sure it matches your C# code.