Accidently I found out that Rockbox crashes on startup if the file it played before shutdown does not exist when starting again.
How did I do it? I connected to the PC via USB and rearranged some direcories including renaming. The file last played was in one of the renamed directories. After disconnecting from the PC I shut down the iRiver player. At the next startup it remembered well what it was playing last time, but could not find the file.
In my opinion this is no reason for an operating system to crash. The correct behaviour would be to ignore the resume playback command an stay in stop position, waiting for the user to select a file to be played.