the topBar navigation in the default templates includes links to Widgets, API and Feedback. But if you deactivet these plugins you get an error when clicking these. The Links are provides by a core component. There it lacks a check if the necessary plugins are installed.
Attachment: Patch that add the necessary checks
Submitted a patch to fix the problem.
Partially dupes #677.
In , fixes #999, refs #677 - suppress top bar nav links for disabled plugins