I have a quick solution to share for an issue that took me longer to troubleshoot and resolve than I thought. I was working in a Kentico project (not my usual foray) and created a web part, then a widget to reference that webpart. I used the right directory structure which mimicked that of the web part and the user control in the solution.
Then I went to the Pages application, opened a page and picked a widget zone to place this widget I created. Unfortunately, my widget, nor its directory structure were there; which was strange, because I could see my widget in the Widgets application.
I noticed that other widgets other developers had implemented were there, so I compared the settings of one of those with mine, and I found the solution. In the Security tab of the widget, I had to check the “Allowed for” box for the “The widget can be used in editor zones” option. After saving that change, I was able to select my widget from the Pages application.
Surprisingly, absolutely no useful results returned from various Google searches on this issue, including the title of this blog post (at the time), so I thought I’d share what I found. Hope this helps.