Could you please share some more details about the error. Looks like this is something related to Reports. Check if there are any reports on Case entity.
I started with dynamics 365 CRM last week . Tried editing the business process "Phone to case". Adeed few steps and one workflow. Also created new entity. Now reverted both the things when I saw erorrs. Now when I try to create a new case and
save it I get error "Server busy" and when I open any case which is already created, shows the above mentioned error.