Right, so I believe this affects any extensions that use the same exact file selector File object uses. I've tried with File, Array, Edit Box, Common Dialog object, Rich Edit Object, all these are affected, probably a lot more, but for example, Picture or Active Picture are not affected cause they use a slightly different selector (custom?).
It's fairly straight forward, open the selector, don't even need to select a file, you can just cancel, after that edrt.exe will not close even if you click the X, it hides the window but keep running in the background, making Fusion unable to Run and Steam unable to reopen Fusion if it's closed (usually forced cause it will think Fusion is still running despite having Fusion itself closed), Steam will just say Fusion is still running and refuse to open it just because of edrt.exe running in the background.
Actually, I'm doing some tests here... I'm not even sure if this is a Fusion issue (I'm using Windows 10 Insider), it seems like actually any software after opening that standard file selector dialog once will not finish the process once closed D: (Notepad for example, tried on it and did the same, open a file selector once and it will not end the process after closing it)
I'll report this to Microsoft, I guess there's not much Fusion could do about it, UNLESS the Run button could also kill the runtime process before trying to execute it again, as a fail-safe feature...
But I've seen other users having this problem as well, I guess it must be a change on Windows or something if this do not happen on non-Insider Windows 10 versions...
I think you should take my suggestion and make the run button kill the runtime process (edrt.exe and the others) before launching it so the error never happens again... Since closing the application will reenable the Run button despite the process is still running in the background.
Cause if Microsoft don't fix this, soon they will merge Windows 10 Insider with the stable release, meaning this issue will affect all users...

