The
core templates (
Text, Document, Contact, Search) templates can't be deleted, nor can the
Appointment or
Task derived templates be deleted since they are used by
Outlook sync nor the
Folder template as it used by
file/folder synchronization.
Actually, as some users have discovered, you can use the
Link/Copy/Move dialog to "move" the non-core templates listed above to another location (which causes them to cease being templates)... Realize that doing so will not actually "delete" them and will probably "break" the related process listed above...
Doing so with the core templates will likely break your urd file (which a full Repair should fix - but no guarantees!).