Scary thing happened to my X5. Was listening to 'the Dark Knight Rises' soundtrack (ALAC 16/44.1 CD rip) and the X5 locked up at the end of the album.
Tried holding the power button (for around 20 seconds). Nothing.
Tried the rest hole. Nothing.
Pushed every other button in a panic. Nothing.
Hmmmmmmmmm.
Nothing worked until I plugged it in to my iPad charger and turned it on while plugged in.
Boom! Back to life!
Issue resolved for me.
Until now I've really not had any crashes or problems and I haven't heard of this before so thought I'd report it for you guys.
My card is Sandisk 64gb formatted with the X5, no skipping or stuttering issues, including high rez and DSD. I'll check the album for tag or artwork issues.