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Setting breakpoints and waiting when the bug happens so I can see which code segment is at fault wouldn't really work.

I see what you mean, and yeah problems like that are hard to solve. Usually in situations like this I will use a SQL Profiler tool and put filters on it, you should be able to set up filters in a way so that only a update / insert is found where some_field = some_value (like I would do with a conditional breakpoint, except in this case its at the global database level). At least then you know the time and the parameters and stored proc that's getting called.. and if you log things in your code you can match up the times... But stuff like that is never easily, and likely in this cases you can blame the vendor or outside feed that is giving you your data. That is the cause of many many problems in data driven applications [lol]