I am no expert at resolving Pulse errors so can't help from my limited experiences but here's what I would be checking if I had the same error.
To me the clue is your first line of the error message - Notice: Undefined property: stdClass::$allow in /Applications/MAMP/htdocs/www.bvdn.nl/pulsecore/template/admin/media_upload_handler.phtml on line 16.
I have looked at the media_upload_handler.phtml file and on line 16 the code in my v5.1 code is about 'allowed_file_types' so I would recommend checking on what media file types you are uploading. I would expect a JPEG file to work. From what I understand the following types are default uploadable - txt, jpeg, gif, jpg, svg, png, pdf, zip, csv, xls, xlsx. If your file type is not in the list you would add them in the Settings page.
Happy trying - if I am totally wrong let me know cause that's how I /we learn.