A word of warning…
WD MyCloud 4TB. I upgraded the firmware to v04.00.00-607 after installing (I didn’t know any better at that point). No, I wasn’t happy with the results, and WD tech support was a waste of time.
I downgraded the firmware as described, w/o any problems. However, after rebooting with the downgraded firmware (v03.04.01-219), Twonky wouldn’t start, and the unit generated the “Media server database internal server error. (400162)” message. (Rescanning or rebuilding didn’t work, because Twonky wouldn’t start.)
I re-applied v04.00.00-607, and after rebooting everything (including Twonky) was back to normal.
I’m told that MyCloud was supplied with Twonky v7.2.6; but I have v7.2.8. So my surmise is that, in my case, the v04.00.00-607 update didn’t just update the firmware; it also updated Twonky to v7.2.8. Downgrading to v03.04.01-219 didn’t change that, and there is some incompatibility between Twonky v7.2.8 and FW v03.04.01-219 which prevents Twonky from starting.
Something to consider before downgrading to v03.04.01-219.