"Failed to login" usually indicate that your HPDM Repository configuration is not correct. To confirm this, I need a screenshot of your Master Repository Editor dialog and the Controller.conf in ..\HP Device Manager\MasterRepositoryController\Controller.conf.
ThinCapture Application is local imaging application different from HP Device Manager. It doesn't work with HPDM Agent.
Your guessing should be correct - 4.5 Agent should be from the image you deployed.