When you installed ImageManager, in the setup wizard if you did not specify a password, then the password you should use to connect (using the File menu's Connect menu item) is the single character number zero "0". This password is stored in the text file C:\Program Files\StorageCraft\ImageManager\ImageManager.exe.config
You can stop the ImageManager service (run services.msc to do this) and then alter the contents of this ImageManager.exe.config text XML file to specify a password different than "0" if you like. Then start the service back up and connect using the new password you specified.