Emotional damage and stress to all involved.
I know of someone working giving out some of the screening invites. The "computer bug" they found, thankfully in time to send out late, but valid, invites... was as simple as the training saying "type search for cancer screening*" when it should have been "screening for cancer" and the new system missing the old systems search results due to wording ORDER.
They felt horrible for the mistake, but in reality, how were they to know the system was setup with 2 different search terms (old and new) and did not bring up a per word result (screening + cancer) but only brought up a single term result ("cancer screening" exactly).
*not actual term, as I was not working there so don't remember, and to protect identity etc.