Such behavior might be caused by an unresponsive adb.exe process or conflicting adb.exe processes (e.g. the one used by the Windows client and the one used by some Android management tools such as Samsung Kies). To resolve this issue, close the Windows client, disconnect your device, kill any instances of adb.exe and instances of Android management tools, shown in the Task Manager. Reconnect your device and rerun the Windows client.
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