I don’t know what the solution is to this problem.
I got this error long back. So since it says “failed on COM11”, I thought it has something to do with the PC’s drivers. So I tried connecting the Pixhawk to a different (2nd) PC, and it worked! However, later, I was trying to do the same thing on the 2nd PC, and I got the same error. And sometime later, it goes back to working as normal. So this thing was randomly coming up.
All my other Pixhawk boards work well with either of my PCs, so I assumed something is wrong with the board.