I've been following this project for a while but had no need for it. Decided to give it a try and I was running into the same situation with crashing on downloading.
I have a Motorola Xoom which I just modified the partition of to allow me to run KitKat 4.4.2. This version has the SD card changes to prevent application writes and even though I made the appropriate modification to allow it as follows:
you can edit /etc/permissions/platform.xml and add a group to WRITE_EXTERNAL_STORAGE
Original:
<permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
<group gid="sdcard_rw" />
</permission>
Add the media_rw group:
<permission name="android.permission.WRITE_EXTERNAL_STORAGE" >
<group gid="sdcard_rw" />
<group gid="media_rw" />
</permission>
it seems that this may be responsible for the crashing when downloading; at least in my case.
Changed the download location to Internal Storage and seems to be working fine now.