"ppcx64" is symlink to fpc executable. In my distro, I have it in /usr/local/bin/ppcx64 and it points to /usr/local/lib/fpc/2.7.1/ppcx64.
Paths in your distro can be different, so:
Check if the symlink points to valid fpc executable.
Try run "fpc -iV" in console.
Check Tools -> Options... -> Environment whether the compiler path is valid.