You apologize for dropping your end of the ball, say how it's good that things are up to speed and moving along, and then you try to change the subject, which goes well for about five minutes until she segues right back to the topic. Are you SURE you never got my email? That's really strange. I know I sent it to you! You wash, rinse, repeat all of your previous comments and then try to move on. Again.
Skip ahead days or weeks to when you've forgotten about the miscommunication and encounter this co-worker in the parking lot. Are you SURE you never got my email? That's really strange. I know I sent it to you! Have you checked your spam folder? I know so-and-so says she got it...
The above situation represents a simple example of the co-worker who can't let things go. It may involve a work situation gone wrong, something that was (or wasn't) said in a meeting, a delivery that got messed up, a missing stapler -- the possibilities are endless, really. You, however, tend to work on the "s*%t happens" model of life and moved on a long time ago. Or would like to, if your co-worker would let you. Instead of letting the snafu roll off his shoulders, he's wearing it like a giant chip. How should you handle this type of person?
Well, you can either say something or not. But if you don't say anything, you might find yourself at the company holiday party a year from now when this co-worker brings it up again out of the blue over glazed ham and crumb cake. Are you SURE you never got my email? Really? Just shut up, already! Now you're sitting there seeing red.
This co-worker may be a know-it-all who ultimately needs to lay the blame anywhere else and simply can't accept that, in fact, sometimes things don't go according to plan, wires get crossed, a ball gets dropped, a box doesn't get checked, a train doesn't pull into the station right on time. Hey, it happens. Especially at work. And research concludes that the accusation-prone employee is likely to be younger.
I tend to go by the "two times at bat" rule: Be polite about it a handful of times (yes, I realize I'm probably being far too generous) before firmly saying that it's time to move on. You might re-hash your side of the story one last time and say this is the last time you're ever going to talk about it. Then quickly shut it down ("It's ancient history now, let's move on") if it ever comes up again. You might also say that revisiting the past is hurting the present and making it harder to focus on the future. You know, all that "forward-thinking" business planning stuff.
Dealing with someone who can't let things go could require you to pick up a few new conversational skills and boundary-setting abilities. With any luck, this co-worker will get the message, and it won't require going through your spam folder again.