"start BitcoinQt manually"
1. Make sure Armory is NOT running
2. Goto: C:\Program Files\Bitcoin
3. Double click on bitcoin-qt.exe
what happens? Also, what version of Bitcoin Core do you have installed?
and "passing your custom blockchain path to Armory"?
You stated that your Bitcoin data directory (ie. the folder that has your wallet.dat and all the Bitcoin Core "blocks" data) is in a non-standard custom location (ie. "Running BitcoinCore on an external HD"). Looking at the logs... it is in D:\BitcoinCore
How are you telling Armory where your Blockchain data is? Did you set that in a .conf file? Did you set it in the Armory settings window?