Hey all, I’ve just finished the Bulls and Cows section of the course and wanted to share an error and solution that I encountered a couple of times along the way.
Disclaimer - I don’t actually know if this is the best way to resolve the error, but it worked for me and seemed to be backed up by some googling. 
Basically, it seems like this error occurs when VS can’t access the executable in the solution. This either means that the permissions for the file/folder have somehow been changed, or your program is still open somewhere on your computer.
This had me stuck for ages, until I looked through task manager and saw my program still open! If you can’t see it in Task Manager, you can obviously try restarting your computer too.
It seems like for me, this was caused by the Avast antivirus file/program shields being on. I closed my Bulls and Cows program and carried on coding, but avast half re-opened it in the background once it had finished it’s scans.
Hope this helps someone!
