Well, it only took three of us to sort this particular bug out.
I had a glitch when I was converting files. This caused reports to send out bad data. The bad data then caused the Excel plugin to fall down and crash.
So first, we got the Excel plugin fixed so that it didn't fall down and crash.
Then we fixed one of the methods in the reports to be a bit more bulletproof than it had been before.
Then I fixed the conversion.
Because you have to be able to see what's broken before you can fix it...