I was using a similar workflow, and had trouble making it work too. I'm sure I had the asin correct, and in my case could get past the error and open the book - but sync remained gray (as if I hadn't done metadata correctly).
In my frustration I gave up, only to notice that Amazon updated the Android app - and the new version fully supports the personal documents service (email to device and cloud storage)! Sync works great now for me because of that between Kindles, Android and iOS devices on my mobis - so I'm completely happy to stop doing all the extra work and just use 'email to device'.
Sadly it still looks like the cloud reader and PC installed version don't have personal docs support yet. Here's hoping they add it soon!