I've never had to do this before but someone's cocked up in a pretty massive way that's really pissed off one of the clients where I work and I'm sort of in a position where only I know about it so far, others will find out about it sooner or later and action needs to be taken to stop it happening again. So I think I'm in a situation where I can't not mention it. But I feel utterly terrible.

Plus I don't think she's done anything wrong per se, simply not understood how the system worked. But in any case I feel really bad. I usually do absolutely everything I can to not have to "grass" on colleagues but I don't think I can avoid it this time.

Has anyone else ever had to report other people's cock-ups? Did you feel massively guilty too?