Normally the .t6 file would be BTCUSD_YYYY.t6 for this asset, but you define it like BTCUSD_1h.t6 in your History setting. Is that file available in your history folder?
Your StartDate syntax is wrong, it should be YYYYMMDD
Warning 034: BTCUSD not in asset list
This isn't an 'unhelpful error message', it means that you need to define BTCUSD in your asset list.