I can only give you steps to reproduce it (sorry): here they are:

1 - Open rockbox
2 - Long click Files, then select Show Files, and choose All (this is so you can see the hidden folders, .sounds, etc)
3 - Start any song, and let it play for a few seconds.
4 - Click in the pause button, wait about 5 seconds or so and then click in the same button. It should crash. That works most of the time

Now, not related to that issue at all but if you want to use the player regularly, I recommend you to go to Settings - Sound Settings - Timestretch - and then select Yes. This prevents the music from stalling randomly until you close rockbox (trrrrrrrrr-like sound, lol)