I run into the same issues with nexus7.

Following worked for fixing this.

1 Open Developer option in the Settings menu on your device.

2 Switch off the button on the upper right of the screen.

3 Delete all debug permission from the list of the menu.

4 Switch on the button on the upper right of the screen.

now reconnect your device to your PC and everything should be fine.

Sorry for my poor english and some name of the menus(buttons) can be incorrect in your language because mine is Japanese.

I run into the same issues with nexus7.

Following worked for fixing this.

1. Open Developer option in the Settings menu on your device.

2. Switch off the button on the upper right of the screen.

3. Delete all debug permission from the list of the menu.

4. Switch on the button on the upper right of the screen.

now reconnect your device to your PC and everything should be fine.

Sorry for my poor english and some name of the menus(buttons) can be incorrect in your language because mine is Japanese.