Working on 4.1 ?

Hi @malaiac,

Thanks for posting on the forum.

I am using the Custom Sidebars plugin on my test site having WordPress version 4.1 and it’s working fine for me.

Make sure you have selected at least one default sidebar as a replaceable sidebar by checking the checkbox “Allow this sidebar to be replaced” of it as displayed in the following screenshot.

View post on imgur.com

If it doesn’t work for you then try using any default WordPress theme like Twenty Fifteen.

Best Regards,
Vinod Dalvi