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Windows 7 & Ubuntu installed. Using a bluetooth mouse. Have to re-install it whenever I switch from OS to OS.
When I use my primary OS (Windows 7) I have to remove the mouse from devices and re-install it everytime I switch from ubuntu and vice versa.
Can you install the mouse in both Windows 7 & Ubuntu and see if that works.
One of the OS does not support Bluetooth. Try updating the drivers for the culprit.