First, a little background:
We were doing software development consulting for a large customer. Their project manager/liason was really hot on the new cheap-software-development-in-India thing (it was 1995) and had arranged for one of these groups to build middleware objects based on our specifications. Communication generally wasn't an issue, but we did have one snag.
I had prototyped an object, written the spec, and sent it off to Bangalore as usual. I got the object back a few days later, but couldn't get some of the methods to work. The back-and-forth communication became more and more acrimonious (Me: This &@ thing doesn't work! Them: Learn how to program!)
Finally, I noticed something: all the inoperable methods had a lower case 'L' in them. I rewrote the code, replacing the lower case 'L's with upper case 'I's and it worked. I typically use a fixed font when I write and develop; it annoys some people, but it prevents just this sort of mixup. Apparently, they didn't like the font I used in my document so much that they reformatted it, using a font that shows lower case 'l', upper case 'I' (and incidentally the number '1') all as a vertical line sans serif.
So I wrote the ECO using their favorite font:
"Problem: The following methods are misspelled... Upper case | should be lower case |..."
"Resolution: Change all instances of | to |."
We kept a framed copy of the ECO on the wall for years.