I don't work with this person directly, and I have never met him face to face as he is at a different location. However, when an issue comes up, he emails me with questions and typically copies his managers on it.
On a previous occasion I was helping him debug a hardware issue, and he was reporting some strange behaviour. I made the suggestion to change part of the setup; this change would have eliminated the error (it eliminates the part that can cause the error). He did not respond for a few days and when I inquired about it, he said the problem remained. When I pointed out that this was not possible, he said he was going on vacation. Then a different engineer came around and my fix was implemented.
Today I got another message that reported strange failures using software that has been tested in same scenario before. He then said that when they program firmware B on it rather than A, there is no problem. But firmware B is the one that should have been used in the first place! At the same time, we just finished testing firmware A and it was proven to be stable.
I don't know if he really has no idea what he is working on, or if he just doesn't care. I am not his manager, and all I can do is complain to my manager about this. Do you have any advice on how to handle this? I feel he just sabotages our projects with his complete incompetence. His manager is on all these email chains and should be aware of what is happening, but it is entire possible that he is too busy and doesn't actually read them.