Creating Articles module throws 500 error

I'm creating a module based on the articles template and running into an issue.

When I select the template and click save, I get this on the client:

Uncaught Error: Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500
at Function.Error.create (ScriptResource.axd?d=NJmAwtEo3IqCaBmDBJSsyeJeJow2dA6sa21u4qjmOny0rGnis85GUgePbhjL9zn5l6KvQzz5NwdGBgtC9UF5YfwB-rUHAlFW2jiTsBHaXuZvtdo9uUfUP1bltoFGjLcPzIUnSQ2&t=ffffffffad4b7194:5)

And I get this on the server:

InnerMessage:Object reference not set to an instance of an object.
InnerStackTrace:
at Satrabel.OpenContent.Components.Manifest.ManifestUtils.DataNeeded(TemplateManifest template) at Satrabel.OpenContent.TemplateInit.bSave_Click(Object sender, EventArgs e)

And:

InnerMessage:Object reference not set to an instance of an object.
InnerStackTrace:
at Satrabel.OpenContent.TemplateInit.BindButtons(OpenContentSettings settings, RenderInfo info) at Satrabel.OpenContent.TemplateInit.RenderInitForm()

DNN 9.1