Contacted ACS team member and found some answers.
For the error 'retCode=6', please do the following steps:
Go to Build->Configuration Manager
Under 'Active solution platform', select 'New' (if x86 does not exists)
Set 'Type or select the new platform:' to "x86"
Set "Copy settings from:" to ""
Check the 'Create new project platforms'
Click 'OK' and rebuild the solution.
For the error 'retCode=-2146434967', it means that the smart card has been removed on the reader.
I've tried this with C#. Ive described on my blog : Simple NFC reading system for windows
I used Mifare classic 1K Tags. Hope someone will take the advantage.
Thanks