I cannot go into exact details due to privacy reasons, but essentially the records on a database that tracks our work imply that I made a very bad mistake - or that I am lying - but I am sure that I did neither.
The mistake was work-related involving some form of research and data entry; there is some data missing which I am sure I inserted (and had specifically double checked multiple times) but when checking now it is missing. Figuring out if there was a bug which caused this disappearance of data required a whole day of the tech guys supporting our team, but they found no bug.
The technical guys point the finger at me, my boss sends me a warning e-mail.
When technology incriminates you for something you didn't do, what's the best way to react professionally, and how to convince the boss that even if the computer says so, you are absolutely sure you didn't?
How to ensure that a technical issue you are not responsible for doesn't affect your performance evaluation?
UPDATE: Today I spoke extensively with a more senior IT guy at the company who initially mocked me in disbelief. He then spent less than a minute checking something (the other IT guys were just annoyed like "what a waste of time, we closed this case earlier") and found that there was some bug. Somehow, he was also able to repeat the same error and it was not caused by any of the user's actions.
I am now cleared, but I want to keep this question open for any other situation where people rely on technology to evaluate work/performance... but the technology wrongly makes someone look bad.