FLStudio doesn't play certain instruments, in my case it happened for FPC and Drumpad (on different projects). They show a red name for the WAV file's name (which obviously means it is not there.
However, when I press ...
FL seems to have lost that connection. That folder no longer appears in the Brower.
More importantly, when I open a tune that uses those samples, FLStudio says it can't find them. Even when I then ask it to search ...