Missing "android." in front of [IntentFilter(new string[] { "appwidget.action.APPWIDGET_UPDATE", BluetoothAdapter.ActionStateChanged })] stopped it showing up in the widgets list....

What the actual f#ck?!?
Link everything, seemed we had a bit of a 'dll hell' issue for a while. Needs some investigation.
Delete .bak file. Where did that come from?