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On the first run of the windows client, you will be asked to allow through firewall, make sure to allow through firewall. Once done, go to Security Control tab on top, and click on "Set Admin Password
Use admin password on the android device that you want to have access to your computer at anytime without being asked to password everytime the Android App is launched.
Use User password on the android device that you want to give one time access to your computer. The android device using User Password will not be registered with the windows app. In this case the user will be asked for a password everytime an attempt to connect to your computer is made.
There are several cases that will result in that issue.