If we open ticket list and check ALL (by check-box in left-top of the table) - Delete button will be disabled.
For enable Delete button we should choose any single ticket. And only after this we can check top-left checkbox to chose all tickets.
Hi@Sergey
I tried testing it on my Service Desk and I got the same result. We will report this to our developers as a Service Desk Bug. Thank you for reporting this issue.