Slider height and/or width are not valid or smaller than 50px

I updated my website (www.salonivon.nl) today and now the right sidebar gives this message:

Slider height and/or width are not valid or smaller than 50px

However, i cannot get is solved.
It is in combination with Multiple Sidebars.

Hope someone can help me.

Thanks in advance.

https://wordpress.org/plugins/multiple-sidebars/