What version of OSX are you running? If it's Yosemite, make sure you have the latest update (10.10.4) as Apple fixed a few major bugs that interfered with Dynamic Link.
Next time, could you drag that error window up and away from the text before you take a screenshot? It would have eliminated my need to ask this question and saved you some time
Did AE CC 2015 open fine before the update?
Does AE CC 2014 still open fine?
Have you rebooted your machine recently?
Hi! Where you able to find a way to get After Effects CC 2015 to run on the newest OS X El Capitan Beta #5? Please help!
El Capitan Beta 5 is a beta.
There's every indication that AE 2015 is a beta, perhaps even an alpha level of release.
I'd strongly suggest going back to Mavericks and AE 2014. That's the best platform/combo of AE on a Mac.