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

I’m using the 2014 template, and haven’t made any alterations to it yet.

I got that error message when using the widget first in the Sidebar, then the footer.

Now I’m trying to get it working somewhere (still not sure how) but the error appears in the footer and sidebar, even while it is not being used in any of those areas.

Any thoughts?

https://www.ads-software.com/plugins/weptile-image-slider-widget/