When you provision a Dynamics 365 instance, it comes with a number of system views that may or may not apply to your scenarios. Take, for example, Contacts: No Campaign Activities in Last 3 Months. If you are not into marketing, why would you need one? As tempting as it could be to just go around and whack the system views you have no need for, DON’T.
If another solution, e.g. Dynamics 365 for Marketing, expects this view to be there, then the installation of that solution will fail.
Shan “Smoke ’em” McArthur, Principal PM at Microsoft, explains:
I do want to call out that I notice that many customers attempt to ‘clean up’ their CRM environment by deleting components they think they don’t need that are brought in via system solutions or ISV solutions. We have a mechanism for them to hide forms and views and that is much more preferred to deleting the view as it is very difficult to bring back a deleted view to avoid future updates from the solution owners. It would be nice for customers to know that they can mark views and forms as inactive instead of deleting them – unless they are the owner of those forms and views.
Moral of the story: if you want to get rid of a system form or a view, deactivate them. Or consider building an model-driven app where you can select exactly which views and forms are available to the users.
If you did the unspeakable and deleted one or more system components, and there is no backup for you to restore, log a case with support who should be able straighten up your instance.