Why can`t I open the channel strip?

Glad you got it sorted. I was just going to mention that if the mixer strips are set too narrow, the ‘e’ next to the Fx may not be visible, also the channel strip insert-position control may not be visible. This may in fact have been the actual problem which the update simply seemed to cure. At any rate, you were right in updating regardless; just keep the channel widths in mind should the controls disappear on you in future.