I have a fraction of wmas that are playing back. Then I have some wmas that are not playing back. In the past I have had songs which played back too fast (double speed, probably). These may be ones that are not playing back now. There are two things that have changed in my setup. The Rockbox version (continuously) and the fact that I have added a sd card.
My wmas are from the Internets and 'might' have been changed post-purchase in one way or the other to be playable with Free Software. . .