Have you checked the mouse settings on both computers?

Sent from my iPad

> On 13 Sep 2016, at 12:17 PM, Juliet Kitson <[email protected]> wrote:
> 
> Help please today for some reason both my MacBook Air and iMac have developed 
> mouse problems left and right have swapped and this applies to an external 
> mouse left and right keys don't work properly ,both are running El Capitan 
> latest version.
> Regards Bill
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