Im having a issue with it not finding my runescape client.
Very weird i've never seen the desktop capture return a black screen like that.
It is able to see other windows when you select something else in the dropdown?
Are you running alt1 in some sort of sandbox mode?
Do you also get a black screen when pressing alt+2?
same thing happens with me
Can confirm, same to me.
edit: running as administrator fixed the problem.