Step 1) Upgrade your version of the flash player via this link http://get.adobe.com/flashplayer
Step 2) Clear cache
Go to 'System Preferences', then click on ' Flash Player' (in Other)
Click on 'Camera and Mic' and then "camera and Microphone settings by site…'
This should bring up a list of sites you have visited. Scroll down to www.present.me and in the right hand pane, change the 'Camera and Mic Access' to Allow.
If present.me is not in the list, click the + button and add the site and change the access settings