We are looking today to a disappointing Unity error, that shows sometimes when developing for Android devices.

When you try "Build and Run", sometimes you can get the following error: "Build Failure:Unable to retrieve device properties"

So, here´s the solution:

1- Kill adb.exe process   (ctrl+a+t+supr to open task manager, and "end task" "adb.exe")
2- Restart your android device.

Thats all, your Build and run should be running fine again.