Symptoms

Whenever user try to delete the forms/views not in used, Smartforms will throw this error "One or more items may not be deleted as they are in use"
 

Diagnoses

We made some initial checks and notice that the error message is not depicting the real situation. All the dependent items (SmartObjects, Views, Forms) on that objects are removed. By right deleting that object shouldn't cause any issues at all.
 

Resolution

This was logged as product issue. This was verified fixed in Smartforms 4.6.10. Resolved by upgrade to 4.6.10.