I get that once in a while.

I recreate the file.  It gets corrupted somehow.

If it's something I create in a TTS program, I cut it again.

I don't know what your source is, but if it's something you've downloaded I would download
it again.

For some strange reason, I've also found that if I've used that same file in another
program, like Sony Movie, it won't work in Poser.