this has been covered in a few other threads already.
to sum up.
with the latest version of FLAC (v1.2.1), the way 24 bit files are encoded has changed. This results in much better compression ratios for 24 bit files, however, on the software side of things, many applications still need to be updated.
The two issues that most people post about are (1) issues with foobar playback, and (2) false error messages from archive.org after uploading 24 bit FLACs (encoded with v1.2.1), because the older version of FLAC that the archive uses cannot decode the files, so it automatically assumes an error with the files.
For foobar, the answer is easy. support for the latest version of FLAC is included in all versions 0.9.5.x and higher. For the time being however, this version of foobar is still in beta. That said, I've been using a beta version of foobar for a couple of months now with no issues. So go over and download the most recent beta version, and your foobar/FLAC issues will be over with.
As for the archive (which you didn't ask about), who knows when they'll get around to updating their FLAC support. Hopefully sooner rather than later.