Flash update is flawed.

[TheronJackson]

Your Flash update refuses to complete past 50%, saying that Safari must be closed, when it is not open.

[helpfromsam]

Safari could be running in the background. Go to Applications - > Utility - > Activity Monitor and see if there is any process of Safari and quit it. Also, make sure you close any other programs that might use Safari (for example MenuTab Pro, a fb chat app that also uses Safari).