avrdude: ser_open(): can't open device "/dev/cu.mydev" : Resource Busy

I'm trying to upload the blink script to my Arduino Uno. However, the usb-port appears to be busy. This is all the output I get:

Archiving built core (caching) in: /var/folders/43/7_h5zwcs1csdr2dc635m1yq40000gp/T/arduino_cache_942504/core/core_arduino_avr_uno_51f02b7210b938436b779d1c032618e1.a De schets gebruikt 928 bytes (2%) programma-opslagruimte. Maximum is 32256 bytes. Globale variabelen gebruiken 9 bytes (0%) van het dynamisch geheugen. Resteren 2039 bytes voor lokale variabelen. Maximum is 2048 bytes. avrdude: ser_open(): can't open device "/dev/cu.mydev": Resource busy

I've tried all solutions I could find on internet, but they haven't solved my issue. The main difference with my error and online solutions/errors is that I only have this error. Other people experienced extra errors which enabled the debugging of the problem.

Can anyone help me please?

I think my available serial ports were insufficient or something. I installed the ch45* driver which allowed an additional device showing up. Here's the download: http://www.wch.cn/download/CH341SER_MAC_ZIP.html

Then I selected this port and I finally could upload.