I also had the same problem TWICE. I tried everything there was to try, reset my settings, change the battery, the sd card, and nothing worked. Then one day without me having done anything, it came back.
Now this is the second time that this happens to me and the problem persists. But now I know exactly when this does happen.
It happens when you tilt the screen and use the flash at the same time. Not always, but on occasion. That's what happened to me on both times it did this.
I think the sensors that control the flash and the modes on the OM-D are neighbors and on the top left at the back of the LCD screen. My assumption is that there might be a problem when some pressure is applied there while tilt the LCD screen. To get rid of the problem, I try to tilt the LCD while using the flash thinking that the problem will go away (and afterwards, if the problem fixes itself, I would avoid doing that). It din't work for me so far - maybe it could work for you.
If anybody has a solution, a fix for this problem, I would be much obliged.